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STEAM ENGINES
A THOROUGH AND PRACTICAL PRESENTATION OF MODERN
STEAM ENGINE PRACTICE
• . • ■ -
BT
LLEWELLYN V. LUDY, ME.
FBorsaaoR or experimental enoineerinq, purdue univerbitt
AMKSICAN 80CZETT OF MECHANICAL ENGINEERS
ILLUSTRATED
AMERICAN TECHNICAL SOCIETY
CHICAGO
1917
» •
COPTRIOBT, 1912, 1917, BT
AMERICAN TECHNICAL SOCIETY
COPYRIGHTED IN ORSAT BRITAIN
ALL RIQBTS RE8KRVKD
i
INTRODUCTION
THE qi^em steam engine, whether it be the majestic Corliss,
whioh so silently operates the massive electric generators in
one of ouf municipal power plants, or the giant locomotive which
pulls the limited at sixty miles an hour, commands our unstinted
admiratiop. And yet every movement is so free and perfect in
its action, every function is performed with such precision and
regularity) that we lose sight of the wonderful theoretical and
mechaqical development which was necessary to bring these
machines to their present state of perfection.
4 Thi genius of Watt, the "father'' of the steam engine, was so
great that his basic conception of this, his greatest invention, and
of ni^y of his minor discoveries in connection with it, remain
almoft as he gave them to the world over a century ago. Yet he
was to far in advance of the mechanical development of his time
that his workmen could not build engine cylinders nearer true
thv& three-eighths of an inch. Modem builders demand an
aoffuracy of at least two-thousandths of an inch — almost two
hundred times greater.
f But -mechanical skill is not the only particular in which prog-
ress had been made. Many minor but important improvements
have been brought about by a careful study of the theory of heat
engines. The reduction of enormous heat losses, the use of super-
heated steam, the idea of compound expansion, the development
of the Stephenson, Walschaert, and other valve gears — all have
contributed towards making the steam engine well-nigh mechan-
ically perfect and as efficient as is inherently possible.
4 The story has been developed from a historical standpoint and
along sound theoretical and practical lines. It will be found
absorbingly interesting and instructive to the stationary engineer
as well as to all who wish to follow modem steam engineering
development. The material is particularly adapted to home
study. If, therefore, the book should prove of real value in
stimulating the interest of the trained man or the layman in the
technical developments of the day, the publishers will feel that
its mission has been accomplished.
<29635
Ki*mi
CONTENTS
PAGE
Development 1
Early history 1
Parts of steam engine 7
Types and construction 25
Classification 25
Simple engines 26
Compound engines 26
Stationary engines 31
Farm or traction engine 50
Locomotive engines 61
Water pumps 67
Special engines 73
Marine engines 74
Types of engines 75
Engine details 81
Propulsion 88
Propellers 90
Management of marine engines 93
Mechanical and thermal efficiency 105
Low thermal efficiency inherent 105
Losses in practical engine 107
Radiation 108
Cooling by expansion 109
Steam condensation and re-evaporation 109
Exhaust waste 110
Clearance Ill
Friction Ill
Operation economies Ill
Multiple expansion 112
Jacketing 114
Superheating 116
Condensers 123
Analysis of engine mechanisms 139
Crank effort f 139
Flywheel 140
Governor. 146
CONTENTS
PAGE
Brection of steam engines 158
Operation of steam engines 161
Engine specifications 169
Selecting an engine 169
Drawing up specifications 169
Contract 174
Engine costs 175
Relative cost of operation items 175
Annual operation expenses 176
Engine tests 177
Importance of tests 177
A. S. M. E. code 177
STEAM ENGINES
PART I
DEVELOPMENT
Early History. In the study of this subject, it is thought advis-
able to review the historical development of the steam engine in
order that a broad conception of it may be obtained. It is not
intended, however, to give the history of the steam engine in detail —
although it is an exceedingly interesting one, which would be bene-
ficial for any one to re\aew — but rather, a short r&um6 in order
that the student may be prepared for a detailed study of the mod-
ern engine.
The first steam engines of which we have any knowledge were
described bv Hero of Alexandria, in a book written two centuries
before Christ. Some of them were very ingenious, but the best
were little more than toys. From the time of Hero until the sev-
enteenth century little progress was made. At this time, however,
there was a great need of steam pumps to remove water from the
coal mines. In 1615, Salomon de Caus devised an arrangement,
consisting of a vessel having a pipe leading from the bottom which
was filled with water and then closed. When heat was applied to
the vessel, steam was formed, which forced the water through the
discharge pipe.
Later an engine was constructed in the form of a steam tur-
bine, but was unsuccessful, and the attention of the inventors was
again turned to pumps.
Savery. Finally Thomas Savery completed, in 1693, the first
commercially successful steam engine. It was very wasteful of
steam as compared with engines of today but, as being the first
engine to accomplish its task, it was successful. Savery's engine,
Fig. 1, consisted of two oval vessels Ai and ^2, placed side by side
and in communication with a boiler Bi. The lower parts were con-
STEAM ENGINES
nected by tubes fitted with suitable valves. In operation, steam
from tbe boiler was admitted, say, to the vessel At and the air driven
out. The steam was then condensed and a vacuum formed by let-
ting water play over the surface of the vessel. When valve 1 was
opened, this vacuum drew water from below until the vessel was
full. The valve was then closed and steam again admitted by
valve ^, so that on opening valve S the water was forced out through
the delivery pipe C. The two vessels worked alternately. When
one was filling with water, the other was open to the boiler and
was being emptied. Of the two boilers Bi and B», one supplied
steam to the oval vessels and the other was used for feeding water
Early Eorm of 8l«am Piunpini EociM
to the first boiler. In operation the second boiler was filled while
cold, and after a fire had been lighted under it, acted like the vessel
used by Salomon de Caus and forced a supply of feed water into
the mun boiler.
A modification of Savery's engine — the pulsometer shown in
Fig. 2 — is still found in use in places where an ordinary pump could
not be used and where extreme simplicity is of especial advantage.
Its valves work automatically and it requires very littie attention.
A serious difficulty with Savery's engine resulted from the fact
that the height to which water could be raised was limited by the
pressure which the vessels could sustain. Where tbe oune was
STEAM ENGINES
very deep it was necessary to use several engines, each one raising
the water a part of the whole distance. The consumption of coal
in proportion to the work done was about twenty times as great as
that of a good modem steam engine. This was largely, though not
entirely, due to the immense amount of steam which was wasted by
condensation when it came in contact with the water in the oval
vessels.
Newcomen. The next great step in the development of the
steam engine was taken by Newcomen, who in 1705 succeeded in
developing a scheme which prevented contact between the steam
and the water to be pumped, thus
diminishing the amount of steam
uselessly condensed. He intro-
duced the first successful engine
which used a piston working in a
cylinder.
In Newcomen's engine, Fig. 3,
there was a horizontal lever A,
pivoted at the center, carrying at
one end a long heavy rod B which
connected with a pump in the mine
below. A piston C was hung from
the other end of the lever and
worked up and down in a vertical
cylinder D, which was open at the
top. Steam acting on the lower
side of the piston, at atmospheric
pressure, was admitted from the boiler to the cylinder, and as the
pressure was the same both above and below the piston, the weight
of the heavy pump rod raised the piston. A jet of water in the cylin-
der condensed the steam and formed a vacuum. This left the piston
with atmospheric pressure above and very little pressure below
(a partial vacuum), so it was forced down and the pump rod
raised again. Steam could again be admitted to the cylinder; the
pump rod would fall; and the process could be continued indefinitely.
In the days of Newcomen it was very difficult to obtain good
workmanship. For this reason it was often necessary to make
the cylinders of wood. In order to prevent steam from blowcft%
Fig. 2. Pulsometer
4 STEAM ENGINES
around the piston, or air from leaking in where steam was being
condensed, it was custoaiary to keep a jet of water playing on the
top of the piston.
One great trouble with all of these en^nes was that some one
was required to open and close the cocks, and boys were generally
employed to do this work. One boy, in order to get time to play,
rigged a catch at the end of a cord which was attached to the beam
Steun PiimiHiig Encine
overhead, and this did the work for him. By making the valves in
this way automatic, made it possible to dispense mtfa the services
of the boy and at the same time greatly increase the speed of the
engine.
The Newcomen engine was improved slightly from time to
time by different inventors and was very extensively used until the
time of Watt, a very few of them still being in existence today.
While this engine was a success and a gre^t improvement over its
STEAM ENGINES 5
predecessors, it was still very large, wasteful, and heavy in com-
parison with the work done, and the cylinders, .vhen made of iron,
were simply cast and not bored, thus leaving a rough, inner wall.
Watt. In the year 1763, a small model of a Newcomen engine
was taken to the shop of an instrument maker in Glasgow, Scot-
land, to be repaired. This instrument maker, whose name was
James Watt, had been studying steam engines for some time and
he became very interested in this model. He was a man of great
genius, and before he died his inventions had made the steam engine
so perfect a machine that there has been but one really great improve-
ment in it since his time, namely, compounding.
He found that to obtain the best results it was necessary, ^^first,
that the temperature of the cylinder should always be the same as
that of the steam which entered it; and second^ that when steam was
condensed it should be cooled to as low a temperature as possible."
All improvements in steam-engine efficiency have been in the direc-
tion of a more complete realization of these two conditions.
In order to keep the cylinder nearly as hot as the entering
steam. Watt no longer injected water into the cylinder to condense
the steam, but used a separate vessel or condenser. He made his
pbton tight by using greater care in construction, so that it was
unnecessary to have a w'ater seal at the top. He then covered the
top of the cylinder to prevent air from cooling the piston. When
this was done he could use steam above the piston as well as below;
this made the engine double acting.
Also, in the effort to keep the cyUnder as hot as the entering
steam, he enclosed the cylinder in a larger one and filled the space
between with steam. This was not often done, however, and only
of late years has the steam jacket been of much advantage. Also,
the steam was used expansively, that is, the admission of steam was
stopped when the piston had made a part of its stroke; the rest
of the stroke was completed by the expansion ojf the steam already
admitted. This plan is now used in all engines that are built for
economy.
Other inventions made by Watt on his steam engines were: a
parallel motion, that is, an arrangement of links connecting the end
of the pbton rod with the beam of the engine in such a way as to
guide the rod almost exactly in a straigVit ^ii<&\ ^ iTwcWiU •w^.tft Vst
6 STEAM ENGINES
regulating the rate of admission of steam; and a centrifugal governor,
which controlled the speed of the engine shaft by acting on the
throttle valve. Watt's engine as finally developed is shown in
Fig. 4.
Watt saw that by using high-pressure steam he could get more
work from it; but as it was not possible to make a very reliable
Fi|. 4. Fiu) Form ot Wi
boiler he never used a pressure of more than seven pounds per square
inch above the atmosphere. About the year 1800, comparatively
high pressures came more into use and the non-condensing engine
was introduced. In Watt's engine, and all those preceding his, a
vacuum was produced in front of the piston by condensing the steam,
and either the atmosphere or steam at atmospheric pressure pushed
STEAM ENGINES 7
it through the stroke. In the non-condensing engine, using high-
pressure steam, the space in front of the piston could be opened to
the atmosphere at exhaust and, although the atmospheric pres-
sure resisted its motion, the pressure of the steam behind the piston
was still greater than that of the air. These engines were much
more simple than the condensing engines, as they required no con-
denser.
Compound Pumping Engine, About this time what would
now be called a compound engine was introduced by Hornblower
and later by Woolf. It had two cylinders of different size, steam
being admitted into the smaller one and then passing over into the
larger. Only a little expansion occurred in the small cylinder and
much more in the larger one.
About the year 1814, Woolf introduced a compound pumping
engine in the mines of Cornwall, but a simpler engine was later intro-
duced and Woolf's engine fell into disuse. This later engine became
known as the Cornish pumping engine and was famous for many
years because of its economy. It was the first engine ever built
that could compare at all with modern engines in the matter of
steam consumption. It consisted of a single cylinder placed under
one end of a beam from the other end of which hung a heavy rod
which operated a pump at the foot of the shaft. Steam was admitted
to the upper side of the piston for a short portion of the stroke and
allowed to expand for the remainder of the stroke. This forced
the piston down, lifted the heavy pump rod, and filled the pumps
with water. Then communication was established between the
upper and under side of the piston, exhaust occurred, and the heavy
pump rod fell, lifting the piston and forcing the water out of the
pumps. Steam was cut off at about three-tenths stroke, and the
piunp made about seven or eight complete strokes per minute with a
short pause at the end of each stroke to allow the valves to close
easily and the pumps to fill with water. These engines needed great
care and were in charge of competent men, to whom prizes were fre-
quently given for the best efiiciency, which doubtless accounts for
thpir wonderful performance.
Parts of Steam Engine. Leaving the historical side of the steam
engine let us now turn to the modern simple steam engine and study
briefly its construction. Figs. 5, 6, and 7, will serv^ Ici '^Jiw^Xx^^ ^
8
STEAM ENGINES
horizontal, center crank engine, all the more important parts being
numbered. The function of the various parts will be considered in
detail later in the work.
Referring to the numbers in Figs. 5, 6, and 7, the names of the
parts are shown in the following list:
List of Parts
Sub-base 1
Frame S
Main bearing caps 3
Main bearing liners 4
Cylinder 6
Cylinder head 6
False head cover 7
Valve chest head (head end) 8
Valve chest head (crank end) 9
Piston 10
Piston rings 11
Piston rod 18
Piston rod nut (piston end) 13
Piston rod nut (crosshead end) 14
Piston rod stuffing box lo
Piston rod gland 16
Crosshead 17
Crosshead shoes 18
Crosshead adjusting screws 1!)
Crosshead pin 20
Crosshead pin nut 21
Cross pin washer H^
Connecting rod S3
Connecting rod bolts 24
Connecting rod strap 25
Crosshead pin box 86
Crosshead pin box w^edge 87
Adjusting screws 88
Crank pin box 89
Crank pin box wedge 30
Adjusting screws 31
Crank disks 38
Crank shaft 33
Flywheels 34
Valve pistons 35
Valve rings 36
Valve cages 37
Valve rod 38
Valve rod nuts (valve end) 39
Valve rod nuts (ram end) 40
Valve rod gland 41
Ram box 48
Ram box caps 43
Ram 44
Ram pin and nut 4^
Ram pin cap 4^
Eccentric rod connection 47
Eccentric rod 4S
Eccentric rod nut (ram end) 4^
Eccentric rod nut (eccentric end) SO
Eccentric 51
Eccentric strap 58
Dash plate 53
Dash plate gland 54
Doors 55
Door handle 56
Door clamps 57
Oil hood 58
Oil hood handles 59
Eccentric oil boat 60
Valve rod oil boat 61
Oil vent 68
Sheet steel lagging 63
Drain cocks 64
Shaft governor 65
Sub- Base, The sub-base 1, Fig. 6, is made of a good grade of
cast iron and is usually heavily ribbed and made high enough to
permit the wheels to clear the floor. The sub-base is often omitted
with engines of large size, the engine being set upon a concrete base.
Frame. The frame 2 is the element or link by which all of the
parts of the engine are held in place, so that their relative positions
STEAM ENGINES 9
are always maintaiiied to the end that their proper functions may
be performed. The frame is a heavy, substantial casting so designed
ng. S. PUn Vie* o( Modern Simple Engine
that it is strong enough to take all the stresses put upon it. The
type, size, and details of the frame \arj' with the type and size of
F!c. «. ffidc EtevBtioi; at Modarn Kmple
the engine of which it is a part. Usually the lower guide, valve rod
guide, and seats for the main bearings are cast integral with vt. \.\^
10
STEAM ENGINES
small sizes the cylinder is frequently cast Integral with the frame.
ProviMon is always made for adjustments necessitated by any wear
of the frame or parts attached thereto. It is to be noted in Fig. 6,
that the frame crank case S is coimected with the crosshead guide.
It frequently has an opening into the sub-base, thus permitting the
oil from the crosshead, guides, and crank to drdn into a suitable
receptacle in the sub-base, from which it is taken by means of a difdn
cock conveniently located in the side or end. The crank is enclosed
by a neat, pressed, sheet steel cover, which prevents the oil from
being thrown outward on the floor while the engine is running.
Quite frequently the crank cover is made of cast iron.
Cylinders. The cylinder 5, Fig. 5, is one of the most impor-
tant parts of the steam enpne, for it is in the cylinder that the
energj- of the steam is converted into useful work. The cylinder is
circular in section and is attached to the bed by means of a number
of bolts. It is made of close grain, gray cast iron. The casting
of the cylinder should be done with great care, so as to insure a
casting free of blow-hoies or other defects.
Fig. 8 illustrates the cylinder in cross section as well as show-
ing its contained parts. The cylinder barrel / is accurately bored
STEAM ENGINES
11
and fitted. Inside of this barrel the piston ^ is driven hack and
forth by the steam, which is admitted alternately on one ^de and
then on the other through the ports 13. The piston is connected
to the crosshead through the piston rod 3. The continuous move-
ment back and forth of the piston causes the surface of the cylinder
to wear away, and in order to avoid a shoulder being formed by this
action, the cylinder is counterborcd at each end by an amount
depending on the size of the cylinder. The diameter of the counter-
Cylindrr knd Vklve Mcchaniam Shown in Sectjun
bore SS is usually about one-quarter of an inch larger than that of
the cj'linder proper, depending, however, somewhat on the size of
the cylinder. The stroke of the piston is such that the piston moves
beyond the wearing surface at each stroke, thus preventing any
shoulder being developed in the cyUnder wall.
The cylinder is attached to the bed of the engine by a number
of bolts which are placed through the flanges 23 of the cylinder and
cylinder head. Each end of the cylinder is closed by means of the
cylinder heads 6 and 9. The cylinder head 6 is caV\eA ^Jt\«\iiwS*;. <E3\i.^i!-
12 STEAM ENGINES
der head (head end), and 9 is known as the front cylinder head
(crank end). In the illustration the front head d is a portion of the
frame, but in many constructions it is entirely independent of the
frame. In order to have a steam-tight cylinder, it is necessary to
make a tight joint between the cylinder heads and the cylinder bar-
rel. This is accomplished by turning both surfaces true, then grind-
ing the joints with emery and oil. After the joints are well ground
the heads are tightly drawn up against the cylinder by means of
bolts suitably arranged. A sheet iron jacket 19 is put around the
cylinder, leaving an air space 21 between the cylinder walls and the
jacket. This air space retards the cooling off of the cylinder walls,
hence initial condensation of the steam in the cylinder is reduced.
In some types of engines such as locomotives, this air space is filled
with some non-conducting material such as asbestos. This is also
Pis. 9. PiiKm, ShowiDf Piaton Riiics fur Miking 8l«am-TiKht Joioti
sometimes done by builders of stationary engines. It should be
noted also, that the back cylinder head has an lur space for the same
reason as that ^ven for the space surrounding the cylinder. Since
condensation does take place in the cylinder, some means must be
provided for removing the water, hence the drain cocks 64, fHg. 6,
are pieced in the bottom of the cylinder at each end. The pipe
connection for these cocks enters the cyhnder in the counterbore
near the wearing surface. Any water that may be in the cylinder
will be forced out through these cocks if they are open. Care must
be taken that the cylinder is freed of water, for if it is not, on account
of the incompressibility of water, the cylinder head may be forced
off or other damage residt therefrom. Some cylinders are provided
STEAM ENGINES
13
with relief valves, which automatically open when the pressure from
any cause reaches a certain amount, thus preventing the bursting
of a cylinder head.
Piston Rings. Between the piston 2, Fig. 8, and the walls of
the cylinder there must be a steam-tight joint, so that the live steam
can not pass around the piston and be exhausted before expanded,
otherwise a great waste pf power will be incurred. The require-
ment is fulfilled by having the piston grooved, as shown in Fig. 9,
and fitted with packing rings. These packing rings, commonly
called snap rings, are turned up slightly larger in diameter than the
cylinder and being cut, as shown in Fig. 9, they spring out into the
cylinder, always pressing against
the walls and forming an almost
perfect steam joint. The piston
of every engine is made with two
or more of these packing rings.
The cuts in the rings must not
be placed directly in line with
each other, otherwise the steam
would have a better chance to
blow through. In order to pre-
vent this the joints are always
placed on opposite sides of the
piston. Packing rings are always
made of cast iron, and are usu-
ally turned up to a uniform sec-
tion. The outside portion and the two sides are carefully machined.
Pistons. The piston 2, Fig. 8, is usually made of cast iron,
but sometimes is made of cast steel. It may be a solid disk grooved,
as in Fig. 9, or the central portion may be cored out, as in Fig. 8.
Another type of piston that is largely used in marine and some-
times locomotive service is illustrated in Fig. 10. This is a com-
paratively light cast steel piston, but at the same time a very strong
one, due to its conical construction. It will be noted also that only
the one packing ring 1 is used. This packing ring is much wider
than the ordinary snap ring and is pressed out against the cylinder
wall by a number of single leaf springs being placed between the
body of the piston and packing ring, as shown in Fig. 10 at 2. T^^
Fig. 10.
Part Section Plan and Elevation
of Conical Piston
14 STEAM ENGINES
piston is made with an L-shaped edge 3, a band 4 being bolted on the
open side of the L, thus forming a groove or opening for the recep-
tion of the small springs and the packing ring. The connection of
the pbton rod to the piston is also cleftrly shown. The rod S has
a tapered end which is forced by hydraulic pressure into a tapered
hole in the piston; the nut 7 b then tightened up and locked by
placing the plate in position around the nut and fastening it with
cap screws. This arrangement insures a lasting connection between
the piston and the piston rod.
It is essential that the piston be as light as possible in order to
reduce the amount of work absorbed in pulling it to and fro, and
also to reduce the wear on the lower portion of the cylinder.
The piston rod 3, Fig. 9, is fitted into a tapered hole in the pis-
ton and secured by means of a lock nut and cotter pin placed on the
back end. Oftentimes the tapered fit is made very tight and the
piston forced on by hydraulic pressure. An older form of attaching
the piston rod to the piston is shown in Fig. 8. In this instance the
rod has a tapered end, which is driven into a tapered hole in the pis-
ton where it is secured by a nut, no cotter pin being used. The
other ^nd of the piston rod is threaded, screwed into the crosshead,
as shown in Fig. 6, and secured by means of a lock nut. In some
constructions the crosshead end of the piston rod is tapered and
secured by a key. Many schemes have been employed by different
manufacturers for fastening the piston rod to the crosshead, all
of which have their advantages and disadvantages. The piston rod,
although usually made of a good quality of open hearth steel, is
frequently made of nickel steel, which possesses great strength.
Stuffing Box and Packing. As the piston rod passes through the
front cylinder head, some provision must be made for making a
steam-tight joint between the piston rod and the cylinder head. This
is accomplished by means of the stufiing box 4f and the gland 5,
shown in Fig. 8. Some form of packing is placed around the piston
rod within the stuflSng box 4 and the gland is forced in by means of
bolts or a secured cap as shown, thus holding the packing in the box
and at the same time crowding the packing tightly against the
piston rod.
The piston packing may be made of woven strands of hemp or
cotton; or asbestos may be used. To insure lubrication of the rod
STEAM ENGINES
16
this fibrous packing is soaked in oil before being placed in position.
In addition to this form of packing there are different compositions
of rubber, graphite, cotton, etc., also various kinds of metallic pack-
ing in use. A metallic packing is made of material such as babbitt
metal, which is a soft alloy of copper, tin, and antimony. This and
other compositions are used for metallic packing, and the metal,
being comparatively soft, wears away much more rapidly than
that of the piston rod. Fig. U illustrates one form of packing,
known as the U. S. Metallic packing. The prindple of operation is
as follows: The babbitt metal rings 2, consisting of three rings cut
in half, provide the packing and are the only parts which come in
contact with the rod. These
rings are forced into the vibrat-
ing cup 6 against the rod, and
are fed down as wear takes
place by the pressure of the
ateam itself. The spring be-
hind the follower 3 is merely l
intended to hold the rings
and other parts in place when
steam b shut off. A ground
joint is made between the flat
faces of the vibrating cup 6 and
the ball joint 4- There is also
a ground joint between the ball
jomt 4 and the gland 7. The *'"'^"*
combination of the sliding face of the vibrating cup and the ball joint
permits the packing to follow the rod freely without any increase in
friction should it run out of line for any cause. This is an important
feature, since the wear of the crosshead, guides, piston head, and cyl-
inder produces an irregular alignment of the piston rod, which would
injure the packing to a marked degree, if it was not flexible. The
parts of the packing are held in place by the gland 7, which is bolted
to the cylinder head. A steam-tight joint is made between the gland
and the cyUnder head by means of a copper gasket. The purpose
of the swab cup 5 is to hold in place a swab, which is usually made
of waste, candle wicking, or a braided material, soaked in oil and
(oled from time to time as a means of keeping the piston rod well
16 STEAM ENGINES
lubricated. In addition to this service, the swab catches and retains
a considerable amount of dust and grit which would otherwise find
its way into the cylinder, where it might do harm. It is to be said
in favor of the various so-called rubber
packings, that they give verj' good ser-
vice. The four different styles of rubber
packing illustrated in Fig. 12, are not
composed entirely of rubber, but contwn
other material such as graphite, cotton,
etc. These different styles of packing
are used both on piston and valve rods.
It is to be borne in mind that all which
has been said with reference to the piston
rod is equally applicable to valve stem
packing. The general construction of the
^■alve stem glands, vibrating cups, etc.,
is identical with those of the piston rod.
The same materials are used for the
packing medium and the same watchful
care is required in order to obtain satis-
factory- results. Packing is an important
subject and one which should be care-
P fully looked after. It can not be said
^ that any one particular kind or style of
IH packing is the proper one to use in every
J case, for a packing which may pve very
Sa satisfactorj' results under one set of con-
SB ditions may utterly fail under another.
H For instance, a packing suitable for low
H steam pressures is not efficient where
^ high steam pressures are used, and a
■ V packing that may ^ve satisfaction with
^ .» -L .^^^r.,'- high pressures mav not in any measure
Fig. 12. Typ« of Rubber Parking or"- _ -' _ ■'
meet the requirements imposed upon it by
the use of superheated steam. Each particular installation is, there-
fore, a different problem and must be solved in a different manner.
Valves. In Fig, 8, the valve ft is shown in position. It will be
noted that the valve rests upon the valve seat 14 and works between
STEAM ENGINES
17
the valve seats and the pressure plate IS. The valve 1! is usually
made of cast iron and may be of many different shapes, as will be
seen in the study of the various types of engines. There are, how-
ever, two general types of valves — one, a plain slide or D-valve;
and the other some form of piston valve. While there are many
modifications and combinations of these two types, yet they are
akin to the two tjpes named. The valve in Tig. 8 is of the slide
valve type. It is what is known as a double ported valve, that is,
steam is admitted to the cylinder by two edges of the valve by reason
of the fact that there is an opening through the valve. The pres-
sure plate 1^ is used for the purpose of reducing the area of the valve
exposed to live steam pressure, it being noted that the portion under
the hollow space ~'4 is not in contact with live steam. This reduc-
Metbods of Cooneeting
tion of the exposed area is made in order to reduce the amount of
effort required to pull the valve back and forth, When the surface
of a valve of medium size is considered and an average steam pres-
sure per square inch of ISO pounds is being exerted upon it, some
conception can then be had of the amount of friction that must be
overcome ever>' time the valve is moved across its seat. To elimi-
nate a portion of this negative work is the primary object of the
pressure plate. Pressure plates are of various shapes and designs
depending of course upon the tj-pe of the engine and the valve used.
One of the advantages the piston valve has over the slide valve
is that it is almost perfectly balanced by reason of the fact that iteNm-
18 STEAM ENGINES
surrounds it on all sides, hence there is no excessive pressure on any
part of the valve. It is comparatively light and therefore easily
driven and lubricated. The general form of construction of piston
valves is illustrated in plan in Figs. 21 and 22.
Eccentric, The valve is driven by its connection to the shaft
by means of the valve stem, eccentric rod, and the eccentric. The
relation of these parts is well illustrated in Fig. 13. The valve shown
is an ordinary piston valve with flexible snap packing rings 4 similar
to those previously described for the piston packing rings. In fact,
the piston valve, as the name implies, behaves very much like the
steam engine piston. The two piston ends / and 2 are held together
by the valve rod J. The valve rod has nuts so placed that the pis-
tons are held the proper distance apart. The valve rods, or stems
as they are often called, extend beyond the valve box some distance
and connect with the eccentric rod o. The manner of making the
connection between the valve rod and the eccentric rod varies widely,
this connection being governed largely by the tvpe of engine and
the exigencies of the case. Fig. 13 shows two methods of making
this connection, one being accomplished by making use of a rocker
arm and the other by using a ram. The way in which the rocker
arm 10 is used, is obvious from the figure. The ram 10 is a square
block, working in a l>earing and so constructed that the valve and
eccentric rod can be attached to it. When the ram is used, the
motion is transmitted to the valve in a straight line, hence there is
less strain upon the connecting parts than if a rocker arm was
employed.
The eccentric rod J, in both cases, is attached at one end to the
eccentric strap 6 and at the other end to the ram or rocker arm.
Xuts suitably arranged make the rod secure and at the same time
pro\ide a means for lengthening or shortening the rod as needs
demand. The valve and eccentric rod are usually made of mild
steel turned true and polished.
The eccentric strap 6 is made of gray cast iron, lined with good
babbitt metal for a wearing surface upon the eccentric. The strap
is held on the eccentric by means of the bolts 7. By remo\nng liners
or shims from between the two sections of the strap, adjustments
for wear can \ye made. There are several patented straps on the
market that possess particular features, but the essential elements
STEAM ENGINES 19
of all eccentric straps are about the same. Provision is made for
lubrication by having an oil cup 11 cast with the strap.
The eccentric 8 is mounted on the main shaft 9 and is held
secure in the position desired by means of the set screw 12. Eccen-
trics for large engines are held by means of one or more set screws
and a key. For a discussion of the function of the eccentric, the
student b referred to the instruction book on "Valve Gears."
Steam Cheat. The box 15, Fig. 8, containing the valve and its
parts, is known as the steam chest. The steam chest cover 16 is
held in place by studs which pass through the flanges 17 into the
box. The steam chest is connected to the steam supply by suitable
pipe connections,
steam being turned on
or off as desired by
means of the throttle
valve. When the
throttle valve is
opened, steam passes
into the chest tliruugti
the valve, into the
cylinder, where it is
Fig. 11. Typickl Croashexl and Pin for Lufa Siie Enfiiia
expanded and then ejected through the exhaust opening. The
energy of the steam is transmitted through the piston and piston
rod to the crosshead 17, Fig. 6, thence to the connecting rod 23,
crank |an 33, to the main shaft. In order that these parts nwy
f»operly perform the function of transmitting this energy, a correct
design is highly essential; therefore, a discussion of their construc-
tion is deemed necessary.
Cronkead arid Connecting Rod. The crosshead is usually made
ot sted which forms a connecting link between the ^\9.Xn\i vA «sA
20 STEAM ENGINES
the connecting rod. It is made in various shapes and patterns.
One type is illustrated in Fig. 6. In engines of larger size, the pre-
vailing form of the crosshead used is similar to that illustrated in
Fig. 14. This crosshead consists of a steel casting 1 and two wedges,
or shoes, 2, which fit over a projection on the outside surface of L
These wedges are either cast or forged and serve as a retainer for
a layer of babbitt metal on the outside. It will be noted that there
are oil grooves cut on the surface of 2 in order to facilitate the oil-
ing of the crosshead guides. These wedges are provided with a
nut and bolt 4f whereby adjustment for wear can be made as neces-
sary. Usually there is a slight amount of clearance between the
crosshead and the guides, but it should not be in any case excessive.
The piston rod is fitted into the end 3, as already described. The
connecting rod is attached to the crosshead pin 6, which fits into
the hole 6 and is held in place by a nut. The crosshead pin 6 is
made of a good grade of steel and has a portion B which fits into the
Fig. 15. Solid Forged Steel Connecting Rod
back side of the crosshead, as viewed, the other portion C fitting
into the outside part. \\Tien the pin is in place, the collar D is
adjusted and the nut E tightly drawn. The straight portion A
goes between the sides of the crosshead, and upon it the connecting
rod brasses bear.
There are two general types of connecting rods in use, usually
classified as marine and locomotive. Connecting rods of the marine
type are as a rule used on engines of comparatively short stroke,
while those of the locomotive type' are employed on engines hav-
ing a long stroke.
These rods are forged from open-hearth steel, with solid forged
ends for the crosshead end, and a square end for the crank end in
case of the marine t>T)e; and a solid forged or forked end for the
crank end in case of the locomotive type.
The connecting rod, Fig. 15, is a solid forged steel rod havmg
the ends machined out to receive the brasses. The crank end 1 is
STEAM ENGINES 21
fitted with a brass or bronze box lined with a, good quality of babbitt
metal. The crosshead end 2 is usually, but not always, fitted in a
»milar manner to that of the crank end. Adjustment for wear is
made by means of wedges at each end, as shown at 3. These rods
are usually of rectang:ular cross section, although round shapes some-
times are used, especially on small engines.
The marine type of connecting rod is illustrated in Fig. 16.
The bod) of the rod is forged similar to the locomotive type, as is
also the small, or crosshead, end, but the distinguishing difference
is in the way in which the large, or crank, end is formed. The end
of the rod is enlarged and finished square, and the box containing
the crank bearing which is lined with a good wearing material, b
fastened to the rod proper by means of the bolts. Adjustment for
wear is made by tightemng up the nuts on the bolts.
It will be seen in Fig. 6 that the connecting rod is the connecting
link between the crosshead and the crank S3. The length of the
Fig. le. Muioe Type of ConnKting Rod
connecting rod bears a definite relation to the length of the crank
radius. The ratio of the length of the connecting rod to that of the
crank radius varies in practice from four to eight. Occasionally
conditions demand a greater ratio than eight, but it is seldom less
than four.
Kg. 17 illustrates the connection of the piston, crosshead, con-
necting rod, and crank shaft. The function and construction of the
jMston, crosshead, and connecting rod have been previously dis-
cussed. However, the figure is valuable in that it shows quite
clearly the relation of the various parts to each other. The crank
shaft used on center-crank engines is frequently a solid steel forg-
ing, which includes the crank pin S.
MiaceUan£oua Parts. In order to compensate for the weight of
the connecting rod and brasses it is necessary to put counterweights
on the shaft as shown at 4, Fig- 17. These (;o>a\\jfer««\.^\a «xt
22 STEAM ENGINES
usually heavy castings, machined to sHp over projections on the
crank shaft, and securely fastened thereto by bolts or set screws.
The portion of the shaft marked 1, Kg. 17, fits into the bearings
provided for the main shaft or crank shaft, the length of this bear*
ing portion being the distance between the counterweights and the
collars 5. It will be noted that on one end of the shaft is located a
disk S. Sometimes this disk is forged as a part of the shaft and at
other times it is made separate and forced on by hydraulic pressure.
The purpose of this disk is usually intended to provide a ready
'^u^
>dd Crank Shaft
means of attaching the shaft of an electric generator when a direct
connected plant is feasible or desired. It may be said here that a
direct connected plant offers many advantages over a belt-driven
system. It simplifies the plant, reduces friction, gives greater
reliability, and makes possible more power in a given space.
The projection 6 on the other end of the shaft is the axis upon
which the flj-wheel is forced and held secure by means of a key.
The crank pin 2 should be of such ample proportions as to be safe
against breakage and the heating of the pin or brasses placed upon it.
STEAM ENGINES
All engines are not of the center-crank tj-pe, but many have a
side crank, the crank being a disk or a crank arm fastened on the
end of the main shaft very much in the same manner as the disk 3,
Fig. 17. In this kind of construction the crank pin is usually a piece
separate from the crank arm or crank disk, and is connected to it by
being forced on and then riveted over, or by nuts put on and cot-
tered. In either the side crank or center crank construction, the
distance from the center of the axle to the center of the crank pin
is equal to one-half the stroke of the engine, as for instance, an
18x24 engine has a crank arm of 12 inches in length, which is just
onchi^ of the length of the stroke. In speaking of the size of the
engine it is customary- to mention the diameter of the cylinder first,
that is, in speaking of an
18X24 engine is meant a
cylinder 18 inches in diam-
eter and a stroke 24 inches.
The main bearing 4, I^ig.
7, should be designed with
great care, having liberal
proportions and lined with
anti-friction metal, ham-
mered in place and accu-
rately bored and scraped
to fit the shaft. On small
engines the lower half of the main bearings are usually made
of a part of the frame, the upper half being a removable cap.
Between the upper and the lower portion of the bearing, metal
liners are placed, which afford ready means for making any neces-
sary adjustments.
Large engines have a babbitt lined, quarter-boxed main bear-
ing of ample size. Fig. 18. To provide for both vertical and lateral
adjustments it consists of four parts carefully machined on all sides
and scraped to fit accurately. This bearing is so constructed
that the bottom piece can be removed by siightiy raising the shaft.
The other three parts are removed after taking off the cap. By
use of the adjusting screws 3, the side S and the top 1 may
be properiy adjusted by the sense of feeling when the engine is in
motion.
24
STEAM ENGINES
There are many other types of main bearings besides those
mentioned, but they differ only from those already described in
some of the minor details. The value of these details varies through
wide limits, each builder contending for his own particular design.
A side-crank enpne needs but one heavy bearing, such as that
shown in Fig. 18, as the flywheel end of the shaft, being subjected to
forces acting in but one direction only, requires a much smaller
bearing. This outer bearing. Fig. 19, is called an out-board bear-
ing and is smaller and simpler in construction than the mun bear^
ing. It is supported by a special casting, which has a hollow recess
into which lubricating oil is poured. The shaft carries one or more
small chains or rings which fit loosely on the shaft and dip Into the
.Fia. IS.
oil. Thus it is seen that oil is constantly brought in contact with
the bearing of the shaft. This same scheme of lubrication is also
used for the main bearing. As the different types of engines are
considered, the several types of bearings will be noted and discussed.
The belt wheels 34, Fig. 5, serve a two-f(»ld purpose — one as a
governing device, the value of which will be discussed later, and the
other as a means of storing up energy* while the piston is in mid-
stroke, where the crank effort is greater than the resistance to be
overcome. The belt wheels act as a flj-whecl and give up this
energy at the ends of the stroke, thus enabling the engine to run
over the dead centers. The design of the belt or flywheel is an
important item in the proper proportioning of a steam engine. Its
weight and dimensions must be very acurately determined. The
belt wheel, or flywheel, whichever is employed, is made of cast iron
STEAM ENGINES 25
of various sizesy some being cast solid in one piece, others being
cast in two or more sections. In any case the wheel is forced on
the shaft and securely fastened thereto by means of a key and set
screws.
TYPES AND CONSTRUCTION
Classification. Thus far an effort has been made to give the
student some idea of the development of the steam engine and enable
him to become familiar with the various parts and their functions.
The natural sequence to the above study is to make a detailed study
of the several types in use. No hard and fast rule can be given for
classifying steam engines as they overlap in so many instances. That
is to say, a simple engine may be either condensing or non-condens-
ing; it may be high speed or low speed, etc. According to well-
known authorities, various piston engines may be grouped under the
following classes: •
r J.. , f ,. , /Single cylinder
I. Number of cylinaer8<,- T.. , ,. j
•^ IMultiple cylinder
Fixed cylinder
II. Construction of cylinders <
Vertical
Horizontal
Inclined
.- i_i 1- J J Oscillating
[Movable cylinders p °
III. Action of steams T^ , , ^.
IDouble acting
Direct acting
IV. Transmission of steam power
Indirect acting
with balance lever or beam
without balance lever or
beam
Professor R. H. Thurston in his book entitled "A Manual of
the Steam Engine" classifies steam engines according to their pur-
pose and use, as follows:
TO... Ml • [Moderate speed
I. Stationary mill engines <„. , ,*^
II. Agriculture engines
III. Portable and semi-portable engines
IV. Road locomotives
V. Railway locomotives
TTT T>„ fCrank and flywheel
VI. Pumping engineajj^j^^ ^^^^
\rtj xjt (Paddle engines
VII. Marine engines s^ .
(Screw engines
VIII. Special types
26 STEAM ENGINES
The same authority further classifies engines according to their
structure, as follows:
- -^ . /simple
^ ^Compound
Direct acting
II. Position of cylinder^
Beam
Vertical
Inverted
Horizontal
Inclined
III. steam fS*"'***'°«7 .
[Non-condensing
IV. Prc88ure|p8*' ^^"^
[Low pressure
,» TV X x« /Reciprocating
V. Piston actions,,., ^^. ^
[Vibrating
VI. Steam turbines
VII. Rotary
trxTT /-I X- /Direct connected
VIII. Connections^ ,
[Geared
TV /^ 1 J.' J Jet condensing
IX. Condensation <o , , .
[burface condensing
They are frequently designated by the name of the inventor, designer,
or constructor, as the Watt, the Corliss, or the Porter engine.
From the last two groupings it is evident there is no sharp line of
demarcation, for in many instances engines of one class have essen-
tial parts similar to those of another type. In this work the classi-
fication outlined in the last group will be taken as a basis for study.
Simple Engines. The simplest t>T)e of engine is the single
expansion. It has one cylinder and admits steam for a part of the
stroke, expands it during the remainder, and exhausts either into
the atmosphere or into a condenser. Simple engines. Figs. 5 and 6,
are now used only for comparatively small powers, say 200 h.p. or
less, and although more extravagant in the use of fuel than the others,
may still be the most economical financially, if low first cost is an
important item; if they are not run continuously; or if the load
fluctuates widely.
G>inpound Engines. Compound engines have two cylinders
known as the high pressure and low pressure. Figs. 20 and 21. It will
be noted that two different types of compounds are represented, the
one in Fig. 20 being known as a cross-compound, the two cylinders
STEAM ENGINES
27
being parallel, and the one in fig. 21, a tandem-compound en^ne,
the cylinders being in line with each other.
Steam enters the smaller or high pressure cylinder, and then
expands until release, when it is exhausted into the larger cylinder,
where it expands further. The cylinders should be so proportioned
that approximately the same amount of work can be done in each,
which may be accomplished by making the high pressure cyhnder
enough smaller than the low so that when the steam leaves the high
at a lower pressure than when it entered it, the increased volume of
the steam may be taken care of and at the same time the increased
area of the low pressure piston may compensate for the drop in steam
pressure.
Hi
;>
Fif. 20. Typing Ciw-Compound Encine
Besides being economical, the cross-compound has a distinct
mechanical advantage. The two cranks may be set at right angles
so that when one is on dead center, the other is at a position of nearly
its greatest effort. This makes a dead center impossible, and gives
a more uniform turning moment. Then the individual parts may be
made lighter and are thus more easily handled.
When the cranks of the cross-compound engine are at 90 degrees
with each other the low pressure piston is not ready to receive the
steam when the high pressure exhausts; therefore, there must be a
receiver to hold the steam until admission occurs in the low. Such
en^nes are called cross-compound, tiecause steam cross^^ q.n«x ^-t^\o.
28 STEAM ENGINES
one side to the other. Sometimes instead of having the cranks at
90 degrees, they are phiced together or opposite. Tlien the strokes
begin and end together, and the high can exhaust directly into the
low without a receiver.
A tandem-compound en^ne, Fig. 21, has both pistons on one
rod, the high pressure piston rod forming the low pressure tail rod.
Such engines are less expensive because there is but one set of redp-
rocating parts instead of two, but like simple endues they have the
disadvantage of dead points.
Triple ExpaTiaion En^Ties. Triple expan^on en^nes expand
the steam in three stages instead of two. There are usually three
Fif. 21. Section
cylinders, viz, the high, the intermediate, and the low, arranged
with cranks 120 degrees apart. This gives a more uniform turning
moment than a compound. Sometimes there are four cylinders on
the triple expansion engine, viz, one high, one intermediate, and
two low. This arrangement gives better balance and is often used
in marine work.
For triple engines there must be a receiver between each two
cylinders. Kg. 22 shows the essential features of a triple expansion
en^ne.
Quadruple Engiites. Quadruple engines expand their steam in
four stages instead of three. Multiple expansion engines are nearly
^always condensing.
STEAM ENGINES
Cylivder Raiioa. There are several considerations to be remem-
bered when proportioning the cylinders of the multiple expannon
enpnes. The ratio of the cylinders sliould be such that each devel-
ops nearly the sajne power, and the drop in pressure between the
cylinders and receivers should be as small as pos^ble.
There are many formulas in use, some simple, others more com-
plex involving mathematical calculation. A common rule for com-
pound engines is to make the ratio of the cj'linders equal to the square
root of the total ratio of expansion. Thus, if the steam has an expan-
Fis. 2S. SeelioD of EneutUI Features ol Triple Eipuuioa Engliie
tuon ratio of 9, the ratio of the cylinder volumes will be V' 9> or 3 ; that
is, the low pressure cylinder will have a volume three times as great
as the high pressure cj-linder. If the cj'Under ratio is 3 and the
length of the stroke is the same for both, the diameter of the low
pressure cyhnder will be 1 .75 times that of the high pressure cylinder.
Another rule is to make the cylinder ratio equal to the total
ratio of expansion multiplied by the fractional part of the stroke com-
pleted when cut-off occurs in the high pressure cylinder.
Suppose the ratio of expansion is 9, as above, and that cut-off
occurs at one-third of the stroke in the high pressure cylinder, the
ratio of cylinder volumes will be 9Xi, or 3. If cut-off occurs at
one-half of the stroke, the ratio will be 9 X J, or 4.5.
30 STEAM ENGINES
For triple expansion engines the low pressure cylinder is made
large enough to develop the full power if steam at boiler pressure is
used.
The intermediate cylinder is made approximately a mean
between the high and low. The area of the intermediate piston is
found by dividing the area of the low by one and one-tenth times the
square root of the ratio of the low to the high.
The above may be written thus:
Area of high pressure Area of low pressure cylinder
cylinder Cut-off of high pressure X ratio of exp.
. . . , Area of low pressure cylinder
Area of mter. cyl. = . , =:—
1.1 X K ratio of low to high
In general, for triple expansion the ratios of the volume of the
three cylinders are about as follows:
l\: Fj: Ta:: 1: 2.25 to 2.75: 5 to 8
For quadruple expansion engines, the ratios are as follows:
Vii V^i V^: I^:: 1:2 to 2.33:4 to 5:7 to 12
It is self-evident that the compound engines illustrated are of
the multiple cylinder class. They also have fixed cylinders and are
double and direct acting. That is, steam acts on both sides of the
piston, and the power is delivered directly from the piston to the
shaft or flywheel without the intervention of a walking beam or
some other transmitting medium. The engines illustrated in Figs.
20 and 21, are horizontal, whereas the one shown in Fig. 22 is vertical.
A horizontal engine is, therefore, an engine whose cylinder is parallel
to the ground, and a vertical engine is one which has its cylinder or
cylinders perpendicular to the ground. These engines may also be
operated either condensing or non-condensing.
From the foregoing it must be obvious that it is not possible to
classify an engine within narrow limits, so it appears to be more
logical to classify them according to the service for which they are
to be used, as in the second grouping.
Selection of Type. In the selection and design of an engine
there are a great many factors to be considered. The engine must
be as light as possible, and yet must be strong enough to do the work
STEAM ENGINES 31
likely to be imposed upon it. The bearings should be large and
ample in number. Lubrication must be given especial attention if
high speeds are to be used. Lightness of design tends towards small
first cost, which is important, but durability and eflBciency should
not be entirely sacrificed for low first cost. In the course of time the
more expensive engine may prove to be the cheaper as maintenance
and repairs may amount to considerable on a poorly designed and
built engine. For some classes of service, however, the cheap engine
is the one best adapted. For instance, in saw mills, cotton mills,
and for similar class of service, a low first cost simple engine is the
one best suited for the work, because the labor employed to operate
it is often inexperienced and ignorant. In such cases the protection
and care that can be given the engine is poor, hence the lower the
value of the property exposed, the less will be the loss resulting from
the depreciation. On the other hand, if one is selecting an engine
for a lighting plant in a city, he would more than likely select one of
the most improved types of high speed, condensing machines. In
the latter case the first cost would be considerably more than the
one selected for the saw mill, but the increased efficiency of operation,
the slight depreciation, and the reduction in maintenance would more
than compensate for this.
From the foregoing it is evident that there are many factors to
be taken into consideration when selecting a steam engine for any
given service. In the further study of the several different types
the class of service for which each is best suited will be indicated in
so far as it is possible to do so. There are, however, some general
features every engine should possess independent of its class. It
should be simple in construction, having compactness combined with
great strength and durability. It should be well balanced and free
from severe vibration. Accessibility of parts is also an important
consideration.
STATIONARY BNQINBS
Simple Side-Crank Type. Stationary engines for ordinary mill
service, such as machine shops, small power plants, and various
manufacturing concerns, are generally simple engines operating at
moderate speed, having either plain slide valves or piston valves.
There are, however, some cases where compound engines ot xssrArx:-
32 STEAM ENGINES
ate »ze have been installed in ^nular plants in more recent years.
The demand for electric generators has also largely affected the
design of steam engines for small electric power plants. In .speak-
ing of small plants, in this connection, it may be taken as meaning
from 25 to 500 horsepower.
A simple slide valve enpne of the side-crank tj-pe, which has
been largely used in plants where a cheap, efficient en^ne was the
requirement, is illustrated in Fig. 23. This engine has one slide
valve, an automatic or shaft governor, and a heavy flywheel which
is used as a belt pulley. It is built in sizes varying from 9 inches X
14 inches to 22 inches X 28 inches, and develops a horsepower of
Fi«, !3. Simple Slids V»lve Engine of Sida-Crank Type
about 45 to 300 according to size of cylinders, steam pressure used,
and the speed at which the engine is operated.
Lubrication of the cylinders is secured by the use of a sight feed
lubrication attached to the steam pipe. The main and crosshead
bearings are lubricated by oil cups.
This type of engine has been extensively used in cotton gins
and saw mills and in small machine shops throughout the country.
There are, however, several grades on the market, and it may be
purchased for a comparatively low figure where the work to be done
does not demand a machine of high grade. This engine has a con-
crete foundation, is well proportioned, and makes a neat appearance.
STEAM ENGINES
Simple Vertical Type. A simple vertical high speed engine that
is particularly well adapted for isolated lighting plants in factories,
stores, mines, and aboard ships, is illustrated in cross section in fig.
24. It requires little attention, occupies small floor space, and is not
extravagant in the use of steam. The engine is neatly and well
designed. It has a large base, which insures stability and rigidity.
All of the working parts are
enclosed, but readily acces-
sible for inspection and re-
pairs. The frame, cylinders,
valves, pistons, etc., art
carefully made and ad-
justed, and the same gen-
eral types of these various
parts conform to the gen-
eral practice of high speed
engines. It will be noted
from the illustration that it
has a center-crank, auto-
matic governor, and a pis-
ton valve. The lubrication
of the moving parts is ac-
complished by means of a
geared pump located in the
interior of the base of the
frame. This pump forces
the oil through pipes and
grooves to the various bear-
ings. This type of engine
is furnished by the makers
in sizes from 3} inches X 3
inches up to 9 inches X 7 inches for general service. Much larger
vertical engines may be obtained, but are made as a special order.
The engine illustrated is so designed to operate at speeds from 250 to
500 revolutions per minute, depending on the size, and uses steam
pressure from 60 to ISO pounds. Its commercial rating is from 1)
, to 60 horsepower, according to the size of cylinders, steam pressure,
and speed of operation.
rticil High Speed Engine
34 STEAM ENGINES
Advantages of Vertical over Horizontal Type, While the discus-
sion given above has had to do with a vertical engine of rather small
dimensions and power, yet it must be borne in mind that vertical
engines in very large units are built and successfully operated. This
leads to a discussion of the relative merits of horizontal and vertical
engines. At the present time the most common type of engine is the
horizontal direct-acting, that is, an engine whose cylinder is horizon-
tal and whose piston acts on the crank through a piston rod and a
connecting rod. In small engines the whole is often on one bed plate.
Such engines are said to be self-contained. The cylinder is either
bolted to the back of the bed plate or rests directly on it.
In marine work vertical engines are used in almost every case, on
account of the saving of floor space, which is so important in a vessel.
This saving of space is also a ver>' important factor in many other cases,
such as in crowded engine rooms in cities where land is expensive.
A second advantage of the vertical over the horizontal engine is
the reduction of the cylinder friction and unequal wear in the cylinder
of the latter. In the horizontal engine the piston is generally sup-
ported by resting on the cylinder, which is gradually worn until it is
no longer round, causing leakage of steam from one side to the other.
This is entirely avoided in the vertical engine.
Still another advantage of the vertical engine is the greater ease
of balancing the moving parts so that there shall be no jarring or shak-
ing. It is impossible to perfectly balance a steam engine of one or
two cylinders. If it is balanced so there is no tendency to shake side-
wise it will shake endwise; and if it is balanced endwise it will shake
sidewise. The jarring is due to the back and forth motion of the
reciprocating parts and the centrifugal force of the crank and the
connecting rod. The crank can be readily balanced by making it
extond as far on one side of the shaft as it does on the other, but the
piston and the connecting rod are more difficult to balance. The
effect of jarring can be greatly reduced, if the crank be balanced and
the endwise throw made to come in line with the foundation, which
should be heavy enough to absorb the vibration transmitted. In a
horizontal engine this endwise throw not being in line with the
foundation will cause vibration in the engine itself.
In machines that can be anchored down to a massive foundation,
a state of defective balance only results in straining the parts and
STEAM ENGINES
35
causing needless wear and friction at the crank>shaft bearings and
elsewhere, and in communicating some tremor to the ground. The
problem of balancing is much more of consequence in locomotive and
marine engines.
To sum up the general advantages of the vertical engines: they
^.
ftft
1 ^
wm
T^i&\
rt\ '
i
m
1
%
§._- ._g^25jtt:^^^^
1^
s .s.^*^^^H
Fie. 25. Buckgye Vertical Crou-Compounil Knginc
have less cylinder wear, they take up less floor spat't, and they can
be better balanced. In addition to these there arc certain advantages
which vertical engines have for certain kinds of work.
DUadvantages of Vertical Type. The pressure on the crank pta
is greater during the down stroke than d\ii\i\% \.W «.v ■5XT(^«,\«R».^»fc
36 STEAM ENGINES
during the down stroke the weight of the reciprocating parts is added
to the steam pressure, and during the up stroke this weight b sub-
tracted.
Another difficulty is that in large engines the various parts are
on such different levels that they require considerable climbing.
This requires inore aiiendanis and is sometimes the cause for neglect
of the engine. The foundations for vertical engines need to be deeper
than those for horizontal engines, yet they do not need to be as broad.
Buckeye Vertical Qvss-Compound Type. The development of
electrical machinery and the increased demand for power in con-
FL|. ZS. Simplt
gested city locations, where land is very expensive and buildings costly
because of their great height, has been the primary cause of the deveU
opment of large vertical steam engines of various types. The engine,
Fig. 25, represents a vertical cross-compound engine as built by the
Buckeye En^ne Company, which Is especially well adapted to elec-
tric railway and power and lighting plants, when floor space is limited.
The engine may be obtained either as a side or a center crank design.
This engine and simple horizontal engines of the same make are typical
representatives of economical, high speed engines. They are high
^ced, but the economy of operation and maintenance make them
STEAM ENGINES 37
very desirable. The vertical engine illustrated may be obtained in
sizes developing from 75 to 3,000 horsepower. A discussion of the
valve gear used on Buckeye engines is to be found in the instruction
paper on "Valve Gears." It is a double valve, giving automatic
cut-off as distinguished from throttling cut-off regulation.
Corliss Type. A general utility engine of the highest type both
from the standpoint of design and economy of operation and main-
tenance is the Corliss engine. It is to be found in electric railway
power stations; in large and small pumping stations; in blast furnaces
and rolling mills; in textile and flour mills; in machine shops and office
buildings; in technical schools and colleges; and in nearly all kinds of
industrial plants in this coimtry and abroad. The Corliss engine is
built in various types, styles, and patterns of any designed capacity
up to 10,000 horsepower.
Fig. 26 shows the valve connection and manner of operation of
a simple Corliss engine. It will be noted that the engine is governed
by a fly-ball governor which is driven by a belt connection to the main
shaft. This governor is connected to the steam valves by reach rods.
The speed is automatically governed by variation of the point of cut-
off. This engine, as well as most engines of this type, has large well-
proportioned frames, cylinders, etc. Good workmanship and mate-
rial enter into its construction, hence it is known as a high-
priced engine; but, on the other hand, it is perhaps the most econom-
ical in the use of steam.
Valve Mechanism. The distinguishing feature of the Corliss
engine is its valve mechanism, a good view of which may be seen in
Fig. 27. The gear has four valves, the two top ones being the admis-
sion or steam valves and the two lower ones the exhaust valves.
There is a connecting rod 7, Fig. 27, which is connected to the eccen-
tric through a rocker arm, and another rod, as may be seen in Fig. 26.
As the shaft revolves, the rod 7, due to its connection to the eccentric,
moves back and forth, and, by reason of its connection through the
clamp 8 to the wrist plate 6, the latter is made to oscillate. The
wrist plate 6 is attached to the frame by a pivot projection. The rods
9 have a right and left screw adjustment on each end and transmit
motion from the pins 14 on the wrist plate 6 to the steam and exhaust
valve bell cranks 10 and 16, respectively. These valves receive
motion in such a manner as to open and close the ^\:<a» \»j^x^"' «
STEAM ENGINES
The steam valve bell crank 10 is free to rotate on projections of the
bonnet and carries at the end of the lever shown nearly horizontal
the brass hook 3 which engages with the catch block. This catch
block is rigidly attached to the valve lever }3, which is keyed to the
end of the valve stem, the latter transmitting motion to the valve.
Attached to the valve lever 13 is the dashpot piston rod 4- The hook
is so made that it may be automatically tripped when the back part
of the hook comes in contact with a cam which is operated by the
Fi(. 27. Corii» Valve Mochiniam in D«tul
arm 2 connected to the governor by the reach rod 1. The operation
of the mechanism is such that the hook may be diseng^ed at any
point of its travel by means of the cam coming in contact with the
tripping leg of the hook 3 and causing it to rotate on the pin and
move the steel catch out of engagement with the catch block.
The slowing down of the engine, in consequence of reduced steam
pressure or an increased load, causes the catch to hold its contact
longer and the steam to be admitted longer. In the event that the
STEAM ENGINES
39
speed be increased in consequence of increased steam pressure or
diminished load, the hook would be tripped by the cam and the admis-
sion valve would be quickly closed by the vacuum dashpot 5, It
must be evident from the foregoing that the regulation obtained by this
device must be very sensitive to any change of speed or load. The
dashpot 5 closes the steam valve when the hook is tripped by the cam.
The cylinders have four cylindrical holes accurately bored at
the four comers, as is shown 2XII and 12 in Fig. 27. Into these open-
ings the valves are placed with their stems and proper packing devices.
The seats of the valves are circular. The portion of the valve marked
2 and U Fig- 28, is circular, whereas the remaining portion may have
any shape, depending upon the requirements of the design. The
valve stem J-^-^ is also irreg-
ular in shape. The portion 4
fits into the slot 3 of the valve
and round portions 5 and 6
serve as bearings and as means
for attaching the driving
mechanism.
Advantages and Disadran-
tages of Corliss Type. Per-
haps one of the chief disad-
vantages of the Corliss engine is the large amount of floor space
required, a factor which often precludes its use. It possesses
many advantages, however, chief among which may be men-
tioned the rapid and wide opening of the steam and exhaust ports;
shortness and directness of ports, which results m small clearance;
the adaptation of the steam valve to the functions of cut-off valves;
and the location of the exhaust ports at the bottom side of the cylin-
der, thus draining the cylinders perfectly. Each of these various
factors contribute to good engine performance, and their combina-
tion lias resulted in making the Corliss engine one of the most eco-
nomical engines manufactured. It will operate upon from sixteen to
eighteen pounds of steam per indicated horsepower per hour.
Angle-Compound Type. As an outgrowth of the demand for
an engine of high speed and one that will occupy a small space, but
which, at the same time, will be economical in the use of steam, there
has been developed the angle-compound engine shown in Fi^, 2a,
Fig. 28. Corliss Valve and Valve Stem
40
STEAM ENGINES
Balancing. In an ordinary high speed steam engine, the inertia
of the reciprocating parts — namely, the crosshead, piston, and
piston rod — and the crosshead end of the connecting rod, is con-
siderable. If a steam engine is to be installed in office buildings,
apartment houses, or in other houses where freedom from vibration
is a prime requisite, it becomes
almost a necessity for the engine to
be perfectly balanced. On an ordi-
nary recii)rocating engine it is
almost impossible to obtain perfect
balancing for two reasons:
First, because of the angularity
of the connecting rod, which causes
the rate of acceleration of the recip-
rocating parts to be much faster
at one end than the other, therefore,
the counterweight which exactly
Fie. 20. SceiiDO
balances the forces at one end would be either too light or too
heavy at the other end.
Second, the counterweight at all positions in the revolution of
the shaft exerts a radial foree and when the counterweight is above
or below the center of the shaft, there are no reciprocating parts
developing a counteracting force, hence the centrifugal force of the
STEAM ENGINES 41
counterweight exerts a powerful unbalanced vertical force. (This
has been observed a number of times in locomotive practice where
the rails have been bent by the extremely heavy blows of the unbal-
anced forces.)
In tests at Purdue University on their locomotive testing plants
it was clearly demonstrated that the unbalanced vertical forces are
so great at high speeds that the locomotive driver is at times lifted
clear off the track. It is obvious from the foregoing that the ques-
tion of balancing is a serious one, and one that should be carefully
considered. A thorough study of the question would involve con-
siderable time and space and the use of higher mathematics.
The several engine builders who put the angle-compoimd engine
upon the market claim for it an elimination of the balancing difficulty.
As will be seen from the illustration, the angle-compound consists
in combining two engines in such a manner that one crank pin serves
both. The high pressure and the low pressure cylinders are placed
at 90 degrees from each other in the plane of rotation of the crank.
* The horizontal engine is arranged so that it is perfectly balanced
along its horizontal axis, but is, of course, badly out of balance ver-
tically. On the other hand, the vertical engine is perfectly balanced
along its vertical axis, but is out of balance in a horizontal direction.
The above statements are true only when we consider each engine
separately. When the engines are placed together, the unbalanced
effect on one tends to neutralize that of the other. Their relation
is such that the same counterbalance serves for both engines. It is
claimed for this arrangement that there are four points in the revo-
lution where a perfect balance exists and the resultant effect is to
give almost a perfect balance. Another point of interest w^ith these
engines is that there are no dead centers; hence by employing a
by-pass connecting the two cylinders, the engine can be easily started
from any position of the crank.
Summary of Advantages. This type of engine, therefore, pos-
sesses the advantage of good balancing; it occupies about one-half
of the floor space of a simple engine of the same power; and the
compounding reduces its steam consumption considerably below
that of a plain slide valve engine.
Uniflow Steam Engine. A type of engine which has a very
extensive use in Europe, and which is just beginning to \a^ \s^%ss»b"
42 STEAM ENGINES
factured in thia country b the Uniflow engine. Mr. L. J. Todd, in
188G, took out patents in England covering the principle of the
Uniflow engine, but Professor Stumpf of Charlottenburg, Germany,
deserves credit for developing the engine and for making it a prac-
tical success. In Europe the high cost of fuel makes even small
economies in the use of steam of considerable value. The Uniflow
engine was designed to secure better economy in the use of steam
than is possible with other steam engines of equal power. As used
in Europe, the poppet type of valve is almost universally employed,
because of the better results it gives with superheated steam,
which is used practically to the exclusion of saturated steam. The
Uniflow engine is now manufactured in the United States by a few
concerns, the Nordberg Company being one of the first to develop
and build a successful engine of thb type in this country.
Method of Action of Nordberg Engine. A cross-section view of
the Uniflow engine as manufactured by the Nordberg Manufacturing
Company is shown in Fig. 30. Steam comes to the en^ne through
the inlet 8 and is led through the passages shown to either admission
valve A. These valves are of the CorUss type, not only to conform
with American practice, but because, with saturated steam, they give
as go od results as the poppet type and are less expensive to construct.
^PB^^teun is exhausted through a ring of ports cast in the middle of
^jlnder and is conducted away by the exhaust pipe shown below.
STEAM ENGINES 43
Thus it is seen that the piston performs the duty of an exhaust valve
by uncovering and covering these exhaust ports. D is a relief valve
of large size, communicating with chamber B, which is separated by a
bridge wall in the cylinder
head from the live steam
space above. This relief valve
ser\'estwo purposes: first, it
relieves the cylinder of any
water that may get into it;
and second, it opens auto-
matically in case the vacuum
is lost and prevents the engine
from compressing above line
pressure. Also, if it is desired
to run the engine non-condens-
ing instead of condensing, the
relief valve D may be backed
off of its seat, thus gi\'ing the
chambers BB as the additional clearance volume which is required (or
non-condensing operation. The drums ('(' on each side of jS relieve
the cylinder and cylinder heads from the strains caused by the
expansion of the inlet pipe.
hi- :::::
i r - ^'.- '.
" 3 IS-HI
nrcrnlogteflMaLead
'^,r-,r-,t-i't
^rcfnla^ t/ t^iS Loed
Typical IndicaloT Carda. Typical indicator cards for a Uniflow
engine with condensing and non-condensing operation are shown in
Figs. 31 and 32, respectively. Figs. 33 and 34 show economy curves
when operating, condensing and non-condensing. The cards show
the effect of the large exhaust area by the rapid falling off of the pres-
sure as soon as the piston has uncovered the exhaust ports and also
the gradual and high compression which is obtained. TbiK «»:«tfsf££^
44
STEAM ENGINES
curves show th&t an overload of 100 per cent requires only 10 per cent
more steam than for full-load operation when the engine runs con-
densing, and but 12 per cent more when operating non-condensing.
Chief Factor in High Economy. The chief factor in the high
economy of the Uniflow engine is the great reduction of initial con-
densation. Id the ordinary steam engine the piston head and the
cylinder head in particular are exposed to the low temperature of
the exhaust steam, which cools them considerably and leaves them
cooler than the incoming steam. This causes the great loss known
as initial condenaaiion. In the Uniflow engine the exhaust steam does
not pass out near the head of the cylinder, and so does not leave the
Pliwe Tbraufh Ceatnl Porta
cylinder and piston heads coot; and in addition, the compression is
carried to line pressure, so that when a fresh supply of steam enters
the cylinder it meets surfaces of practically the same temperature as
its own. Furthermore, the walls of the cylinder in the Uniflow
en^e are exposed at each successive point in the stroke to tem-
peratures which are more nearly the same than they are in the usual
counter-flow engine; this also helps the engine economy.
Cylinder and Valve Arrangement in Skinner Engine. The form of
cylinder and valve arrangement used in the Unaflow engine, built
by the Skinner En^ne Company, Erie, Pennsylvania, is illustrated
in Figs. 35 and 36. It will be noticed that the steam valves
STEAM ENGINES
46
are of the poppet type and are located on the top of the cylinder.
Exhaust takes place through central ports in the usual way and also
through the auxiliary e;disu8t valves shown on the bottom side.
Fig. 35 shows the piston on head-end dead center with the steam
valve at admission and exhaust taking place through the central
ports. Fig. 36 shows the centEal exhaust ports closed, the steam
valve on the head end closed, and exhaust taking place through the
auxiliary exhaust valve on the crank end.
When the engine is operating non-conden^ng, the auxiliary
exhaust valve for the end in question is opened by the valve-gear
mechanism at the point when the central exhaust ports are just
Tic. 36. Bection of Uuflow Eo^i
closing, and compression commences at about 35 per cent of the
stroke. When operating condensing, the valve-gear mechanism
controlling the auxiliary exhaust is automatically disengaged when
the vacuum reaches a predetermined amount. Under these con-
ditions the auxiliary exhaust valves remain closed and compression
begins at about 90 per cent of the stroke. The construction is such
that if when operating condensing the vacuum should fail, the aux-
iliary exhaust valves are automatically thrown into operation.
American Locomobile. The locomobile is already highly
developed in Europe, particularly in Germany, but in this country
developments have just recently begun. On account ^ ^ \»i^
46 STEAM ENGINES
efficiency, a description of its construction and operation seems
desirable.
This apparatus is really a complete power plant all contained
in a single unit. It consists of a steam boiler with furnace, super-
heater, and reheater; a compound steam engine with condenser and
vacuum pump; a feed-water heater; and a boiler feed pump. It is
now being constructed by different American manufacturers, but that
built by the Buckeye Engine Company will be taken as t>T)ical, since
they were the first builders of locomobiles in the United States.
Details of Power Plant. Referring to Fig. 37, the path of the
gases and steam can be traced through the plant, and some of the
mechanical features can be seen. Consider first the boiler, furnace,
superheater, and reheater. The former is an internally fired, fire-
tube boiler, the combustion chamber being at A and the fire tubes
at B. Beyond these tubes is the circular pipe coil C, which is the
superheater, and still further on is the reheater Z), consisting of loops
of pipe expanded into two headers, as shown. The furnace gases from
A pass directly through B, C, and D, and then out to the stack
through the connection shown in the floor. The boiler is supported
on cradle blocks X, and the superheater and reheater piping is hung
from horizontal beams, as shown.
The steam is led from the dome E to the rear end of the super-
heater and leaves it at the front end, going straight up to the high-
pressure cylinder of the engine. Leaving the high-pressure cylinder,
the steam is carried to the front end of the reheater and, leaving at
the opposite end, is conducted to the low-pressure cylinder of the
engine. From the low-pressure cylinder the steam is conducted to a
feed-water heater and then to the condenser, neither of which are
shown in the figure. In both superheater and reheater, the steam is
made to flow against the direction of flow of the furnace gases so
that the steam will enter the engine cylinder at a higher temperature.
The engine, as can be seen, is mounted directly on the boiler.
The saddle F, bolted to the boiler shell, supports the engine bed, which
is securely fastened to it. The engine frame is permitted to slide on
the saddle 6 so as to allow for unequal expansion between the boiler
shell and the engine frame. At the head end of the low-pressure
cylinder the yoke Y Y supports the cylinder casting.
Fig. 38 shows the relative temperatures of the steam and the
STEAM ENGINES
STEAM ENGINES 49
gas at various points in their respective paths. The figure is self-
explanatory, except that the feed-water heater, condenser, and
vacuum pump shown in the upper right-hand comer are put there
merely for convenience of illustration. In the actual locomobile
they are situated alongside the boiler in some convenient manner.
The temperatures here shown are approximate and would vary, of
course, with different coals, combustion rates, steam pressures, etc.
Fig. 38 also clearly shows the manner in which the waste gases
circulate around the high- and low-pressure cylinders.
,--'
■ik'
2
Z W-
Vff
^"""""uSf'"
^^it'
M^ '■'-.
' "fT5f!» f
-"^fLU r
-■-
5j^,,-^,_st.
•^r-Trr
sfS: ::::
TTmTrtTi ""
t^-..--.-.-
]im_i___
''I
Onpbicft] Kamlta of Looamr
The big saving aimed at in the locomobile is the reduction of
radiation and condensation losses to a minimum. This would mean
of course that a greater amount of work could be generated in the
engine by the burning of the same amount of coal. In tests con-
ducted in this country, the locomobile has generated an indicated
horsepower on less than two pounds of coal, and has used approx*
imately ten pounds of water. Fig. 39 shows graphically the results
of tests, which are remarkable conadering the size of the unit.
General Survey of Stationary Types. The treatment of the
subject of mill or stationaiy engines, in so fat &% \!oft ?«~c>^ ^ '^^^
50 STEAM ENGINES
work will permit, has been covered by the discussions given concern-
ing the plain slide valve engine, the vertical engine of small units,
the vertical engines for large installations, the compound and tan-
dem engines which are being used more and more, and finally by a
consideration of the most economical engine of all, the Corliss, whether
operated simple or compound. In addition to the types mentioned
there are a large number of other makes, which have distinguishing
features and which give good service, but yet the principles enumer-
ated in the types already discussed fulfill all the requirements likely
to be made upon stationary plants. Hence a discussion of other
makes is not thought necessary.
FARM OR TRACTION ENQINB
The advancement of scientific and progressive farmmg has made
the farm engine of more interest and importance than ever before;
in fact, the demands of the active farmers in recent years have taxed
the builders of such equipment to the limit of their output. The
steam engine is used for a large variety of purposes upon the mod-
em large farm, and appears most commonly in the form of the so-called
traction engine. It is used for plowing, digging ditches, building of
roadways, logging purposes, running threshers, and numerous other
purposes. Various types of stationary engines of small power are
also to be found in use on the farm, the small gas engines now hav-
ing been perfected to such a degree that they are rapidly replacing
the steam engine.
General Description. The traction engine is really more than
simply an engine; in fact, it is a self-contained power plant. It con-
sists of a simple or compound en^e, a boileur for supplying the steam
required by the engine, and the transmission mechanism, together
with all the auxiliaries necessary for a complete power plant. A good
type of a general utility traction engine is shown in Fig. 40. It con-
sists of a boiler of the locomotive type, carried by four wheels, the
two front ones serving as a means for guiding, and the two rear
being the ones which receive the power and known as the driving
wheels. In order to prevent the slipping of the rear wheels when
doing heavy hauling, they are made with heavy projecting lugs or
cleats which are forced into the ground by the weight of the machine.
The engine, which is mounted on the side of the boiler, as may be
STEAM ENGINES
52 STEAM ENGINES
seen in the illustration, is a plain slide valve engine of the side-crank
type. The speed is regulated by an ordinary fly-ball, centrifugal
governor. The construction of the various parts of the engine are
similar to those previously described in this work. The same
watchful care should be given to the lubrication, operation, and
maintenance of this engine as to any other, when economy, durability,
and reliability are desired. It should be noted that both cross-com-
pound and tandem-compound engines are used as well as simple
engines in this class of service, and that various types of valves find
application.
In order to make dear the construction and operation of the
traction engine, a view showing the rear wheels, platform, and side
tanks removed is shown in Fig. 41. The means provided for guid-
ing, reversing, and driving this engine is clearly illustrated. It is
evident that the type of boiler used is similar to that of the locomo-
tive boiler, having a narrow fire box. It has an extended front end 1
and stack 2 for carrying away the gases of combustion. The boiler
is mounted upon the front wheels through the pivoted pedestal con-
nection 3. It is supported on the rear wheels, by having the rear
axle extend beneath the fire box, or by having the supporting ele-
ments riveted to the side sheets as in Fig. 41.
Operation of Plant. Reversing Mechanism. The operation of
the plant is about as follows: If the engineer desires to go forward
the mechanism is placed in forward gear by means of the reversing
lever 29, the reversing being accomplished by means of a swinging
eccentric, which can be thrown across the shaft at the discretion of
the operator. (On some types of traction engines, a reversing link
mechanism is used.)
Transmission. Having adjusted the reversing gear in accord
with the desired direction, the throttle valve of the engine is opened by
moving the lever SO. The opening of the throttle valve starts the
the engine shaft IS, which carries the flywheel 11. On the engine
shaft behind the flywheel is keyed a small spur gear which is in mesh
with the larger gear 13, which in turn meshes with the gear 14» As
the engine shaft revolves, the small gear in the shaft revolves, which
transmits its motion to 13 and on to the small gear 15, which is
keyed to the shaft driven by the wheel 14- The gear wheel 15, Figs.
40 and 41, is in mesh with an annular gear on the drive wheel U Fig.
STEAM ENGINES
54
STEAM ENGINES
40; hence, by reason of this connection, the large wheel is made to
revolve. The shaft carrying gear wheel 15 extends beneath the
boiler to the opposite side and drives a set of gear wheels which causes
the other driving wheel to revolve with the one just considered.
Running Gear. The axle 16 of the wheel has a sliding head 17
attached to it. This head is free to move up and down in guides
securely fastened to the fire box. This sliding head works against
a spring, which is contained in the box 18. This spring reduces the
shocks to which the machine is subjected when on the road, hence,
' the en^ne is much easier to
ride than it otherwise would
be. In ad<Ution to the easy
riding qualities, it also re-
lieves the parts of the ma-
chine of stresses and struns
due to sudden jolts, which
would be detrimental to the
durability of the machine as
a whole.
Steering Gear. The engine
is guided by the hand wheel
10. It will be noted that a
chain is connected to the
front axle on either side of
the pivotal point. This
chain wraps around a cam
arrangement on the shaft
which carries the small gear wheel 8. The wheel 8 is in me^ with
the worm 9, which may be turned by the hand wheel 10. If the
driver when moving forward should wish to turn to the right, for
instance, he would turn the hand wheel so the wheel 8 would be
driven counter-clockwise, and in so doii^ the chun 6 would be
shortened, the chain 7 lengthened, the wheel 5 would be cut in, and
the machine would turn to the right. If it was desired to go in the
opposite direction, the reverse operation would be carried out, that is,
gear 8 would be revolved clockwise.
It is sometimes difficult to operate the steering gear by hand,
eq>eaally in large traction engines and in places where a heavy load
L
1
M
Friotinn Oow Dsirii
STEAM ENGINES 55
is being driven over rough ground; hence, some engines are provided
with a friction gear device. This attachment, Fig. 42, is exceedingly
simple, and when it is used the engine furnishes power to guide itself.
It consists of a shaft 2 extending from the worm gear / to a bracket
on the side of the boiler in front of the main shaft. On top of this
vertical shaft is a horizontal miter gear S arranged to engage alter-
nately with two vertical gears, one at the right 6 and the other at the
left 4' These vertical gears are on a shaft run by a chain of small
gearing 6 from the engine shaft. They are thrown in or out, at the
pleasure of the operator, by means of a shifting yoke which is worked
by a straight rod extending back to the right-hand side of the engi-
neer. A lever at the end of this rod is within easy reach all the time.
By moving it forward or backward, the engine is guided to the right
or left, as desired. If the lever remains at the center, the engine guides
straight. An extension rod is placed on the rear end connecting with
a hand lever at the left side of the platform, so that the engine may
be guided equally well from either side. To operate this steering
lever requires no appreciable exertion on the part of the engineer.
Friction Clutch. A friction clutch is provided in the flywheel,
which permits the engine to be operated without driving the machine
forward on the road. With the engine running at full speed, the
clutch can be gradually thrown into action, and the machine will
start forward on the road without any sudden shocks. The clutch
is operated by the lever SI, Fig. 41. By disconnecting the engine
from the flywheel, a high speed can be obtained, so that by throw-
ing the clutch in gear quickly the engine is often able to pull the
machine out of difficult places. Oftentimes it is desired to oper-
ate the engine independently of the traction wheels for the purpose
of running the thresher, saw mill, electric generator, or for other pur-
poses, hence some form of clutch is necessary.
Brake, A friction brake is operated by a system of levers and
rods as 19, 20, and 21, Fig. 41. The operator can apply the brake
by pushing downward upon the foot piece on the lever 19. The
amount of air admitted to the fire box is controlled by the two dam-
pers 22 and ^, which may be manipulated by the levers 24 and 27.
Water Tanks. In Pig. 40, large tanks 2, S, and 4y are shown.
These tanks are water reservoirs from which the supply pumps take
water and deliver it to the boiler. Opposite the tank ^ is a bin foi:
56 STEAM ENGINES
holding the fuel, which may be wood, coat, or straw, depending upon
the location and character of work to be done. If the traction engine
is used for threshing purposes, it would have a fire box arranged for
burning straw; whereas if it was being used in a logging camp or a
saw mill, the available fuel would be wood, hence the fire box would
be constructed accordingly.
Boiler. Since it is necessary to have a high-grade, durable, and
economical boiler in order to have an efficient and reliable machine,
it is thought advisable to call especial attention to the type of boil-
ers used in this connection and point out some of their good and bad
features. It was mentioned in the description of the traction engine,
I^g. 40, that a locomotive type of boiler with some modifications was
used. Fig. 43 illustrates such a boiler. It is of the fire tube horizon-
He, 43. Tractkia Boiltr
tal type. The fire box J is of a horizontal rectangular construction
with open grate bars B and ash pit S, below. The fuel, either wood
or coal, is fed through the fire door 5, and the ash ta removed through
the door 4- The products of combustion, such as smoke, hot gases,
etc., pass through the tubes 10 into the front end 12, from whence
they are exhausted through the opening 13 and the smoke stack into
the atmosphere. If straw is to be used as fuel, a brick areh is placed
in the fire box which defiects the gases toward the fire door so that,
after passing over the areh, they are drawn out through the tubes
in the usual manner. It is also necessary to put in different grate
bars where straw is used, as the bars must be closer together so the
fuel will not drop through into the ash pan.
STEAM ENGINES 67
It will be noted that the fire box is surrounded by water legs ff,
7, and 8, and the water and steam space 17. Water is also circulat-
ing around the tubes and is several inches deep above the crown sheet
18, As combustion takes place in the fire box and the hot gases
pass through the tubes, the plates of the fire box and the tubes become
heated. As a consequence, the water in contact with these hot sur-
faces becomes heated also, and steam is formed which rises to the
top of the boiler, entering the steam dome 14 from whence it is taken
by the pipe 15 through a throttle valve to the cylinder. By using
a steam dome a better quality of steam is obtained, because it is so
far above the water level that less water is carried over by the steam
into the steam pipe 15.
This type of boiler has many advantages as well as some disad-
vantages. It has a large amount of heating surface and it is
well distributed. Due to the large amount of heating surface and
the excellent draft arrangement, a high evaporation per square foot
of heatiag surface is obtained. It is well adapted to various classes
of service and operating conditions. Its disadvantages consist largely
in the cost incurred in its maintenance especially in localities where
bad water must be used. When this condition is imposed upon it,
the flues give trouble by leaking around the joints where they enter
the flue sheets 9 and 11, This leakage may at times become trouble-
some and in the end costly if proper preventive measures are not
taken regularly. Some criticism is also made of this boiler on account
of the necessity of using stay bolts in the crown sheet and water legs.
It must be admitted that stay bolts are also an item of considerable
expense in bad water districts where high steam pressures are used.
But by watchful care and manipulation this boiler will give splendid
results and for some classes of seryice it has no equal.
The type of boiler, shown in end view in Fig. 44 and in longitudi-
nal cross section in Fig. 45, is a modification of the well-known and effi-
cient Scotch marine boiler. The boiler consists primarily of a cylin-
drical fire box 1 enclosed by a circular shell. About midway of the
fire box is placed a bridge wall 7, which deflects the hot gases upward
against the shell of the fire box. Ordinary cast-iron grate bars are
inserted as at 4* with the ash pit below. It is to be noted there is
a water space 6, which extends the entire distance around the circular
fire box. Above the fire box there are a number of return tvkbfts. S^
58
STEAM ENGINES
which take the hot gases from the rear end 8 of the boiler to the smoke
stack. The path of these gases is indicated by the arrows. To
protect the rear sheet from the heat of the gases, a protection plate
9 is riveted or bolted to the plate. As steam is generated it rises,
enters the steam dome 12, passes into the steam pipe 13, and on to
the engine.
It ^ould be noted that this boiler contuns no stayed portions
and that all the surfaces are ovular in form and secm^ly riveted.
There being no stayed sur-
faces the circulation of the
water is not interfered with
— which is an important con-
sideration — and the oppor-
tunity for scale and sediment
to collect is greatly reduced,
hence there is less likelihood
of portions of the boiler be-
coming heated to the point
of injuring the boiler or im-
pairing its safety. Still an-
other feature of interest in
the boiler is that the gases
are made to traverse the en-
tire length of the boiler twice
before being ejected at the
stack. This being the case
an opportunity is given for a
greater portion of the heat
contmned in the gases to be
absorbed by the water, thus
securing a higher thermal
efficiency than obtained from boilers of the locomotive type. Having
no stayed surfaces and a small number of flues results in a small
maintenance cost of this type of boiler.
Traction engines run in sizes from about 7\ inches X 10 inches
to 12 inches X 12 inches for single engines, and for compound
engines the common sizes are 5} inches X S) inches X 10 inches to
9J inches X 13 inches X 11 inches. The corresponding horsepower
Fit. **• E^wl View of Modified SooMh
STEAM ENGINES
60 STEAM ENGINES
developed will run between 15 and 100. The speed attained on the
road in miles per hour is about 2) to 5.
Road Roller Type. The traction engine just considered as an
agricultural engine may also be considered as a portable engine or a
road locomotive. A portable engine ts, therefore, one that can be
easily moved about from place to place, or as in the case of the trac-
tion engine it may be mounted upon wheels and self-propelled.
Fit. *B' Sami-PorUble Enciiw
Another illustration of a sioular type is the ordinary road roller, or
road locomotive as it is sometimes called. The principle of its con-
struction and operation is similar to the traction engine, the chief
difference between the road roller, or road locomotive, and the ordi-
nary traction engine being that the two front wheeb of the traction
engine are replaced by a large smooth roller, or cylindrical weight,
which revolves as the engine moves. The drive wheels of the road
roller are also made large, heavy, and contain no cleats or lugs. These
. rollers are used in the making of macadamized or other forms of roads.
STEAM ENGINES 61
Semi-Portable Type. The semi-portable engine is usually
connected with a small boiler and the two together may be moved
from place to place as required. It is not mounted upon wheels but
rather on large wood skids, and is moved by being placed either
in a wagon or on rollers. It is largely used for hoisting purposes in
connection with the construction of large buildings, bridges, etc.
Since the portable and semi-portable engines have no transmis-
sion mechanism, they are lighter and considerably cheaper to con-
struct than traction engines.
A very neat, compact, and serviceable type of semi-portable
engine is illustrated in Fig. 46. It is mounted upon skids so that it
may be easily moved about. The engine is mounted on top of a
Scotch marine boiler, similar to the boiler last described^ and is of
the plain slide valve, center-crank type, with a centrifugal governor.
The boiler is equipped with a pressm^ gauge, water glass, and such
other appliances as are usually found in a boiler room of moderate
size. The boiler used is sometimes of the locomotive type and,
oftentimes, both engine and boiler are of the vertical type. The
smaller units are usually of the vertical type, the larger ones of the
horizontal type. The semi-portable plant is built in sizes ranging
from about 20 to 70 horsepower. If the semi-portable plant, Fig.
46, be mounted on wheels and drawn by horses or some other means,
then it is usually classed as a portable engine as distinguished from
a semi-portable or traction engine.
LOCOMOTIVE BNQINBS
It is not within the province of this work to fully discuss the
modem railway locomotive, but suffice it to say that no other power-
developing unit has been so rapidly developed with such economical
results. Considering the exacting demands made upon a locomotive,
its performance is remarkable. The locomotive consists of two pri-
mary elements, namely, the boiler which generates the steam and the
engines which convert the energy of this steam into useful work by
giving motion to the transmission mechanism.
Boiler. Fig. 47 illustrates a modem locomotive boiler. It con-
sists of a cylindrical barrel and an enlarged rear end which contains
the fire box. The fire box is securely fastened in the boiler shell by
stay bolts and radial stays. A few rows of sling stay^ %.x^ ^j^TSkS^'Cxa^sSk
STEAM ENGINES
t '^'-J ^'
STEAM ENGINES 63
used at the front end of the fire box to allow for expansion and con-
traction of the sheets. The boiler is divided into three distinct
departments, as the fire box A, the water space B, and the smoke
box C. The sheets 4 ^^d 6, which separate these departments, are
known as the back and front flue sheets, respectively. The flue
sheets are drilled with holes to receive the flues.
Fives. In the particular boiler illustrated about 400 2-inch
flues are used. These flues extend from flue sheet to flue sheet and
form a passage for the gases to travel from the fire box to the smoke
box. Surrounding the flues in the space B and surrounding the fire
box is water, which is vaporized into steam due to the combustion
of fuel in the fire box. The total amount of heating surface will
vary from 2,500 to over 4,000 square feet, according to the type and
size of the locomotive. Of this total amount of heating surface only
a very small per cent is furnished by the fire box, there being usually
only about 200 square feet of heating surface contained in the fire
box. It is evident, therefore, that the flues are a very important part
of the locomotive boiler.
Grate Area. The amount of grate area varies from about 40
to 60 square feet. It must be obvious that in order for so small a
grate area to supply sufficient heat to such a large amount of heating
surface there must be a very high rate of coal consumption per square
foot of grate area. A series of tests made at St. Louis during the
Exposition in 1904 demonstrated that the amount of dry coal fired
per square foot of grate area per hour varied from 20 to as high as
130 pounds. These results were obtained from several different
types of locomotives operated imder widely different speeds and
loads, hence the above figures may be taken as approximating the
maximum and minimum consumption under ordinary running con-
ditions. Under these very widely different operating conditions it
was found that the equivalent evaporation per pound of dry coal
varied from 6i to 12 pounds, which compares very favorably with
stationary boiler performance which gives an average evaporation
of about 8 pounds of water per pound of coal.
Mechanical Eflficiency. The mechanical efficiency of a locomo-
tive is also very good. Through a long series of tests conducted on
a well-equipped locomotive testing plant, a mechanical efficiency of
65 to 85 per cent was obtained. The same degree oi ^^^^«tf!:^\i36a.
64 STEAM ENGINES
been obtained in various other tests and under more adverse condi-
tions. The locomotive is also very efficient in the use of steam.
The St. Louis tests showed that simple freight locomotives gave an
average minimum water consumption per indicated horsepower per
hour of 23.67 pounds. The water consumption per indicated horse-
power per hour under maximum load was 23.83 pounds, whereas the
maximum rate was 28.95 pounds. For compound freight locomo-
tives the average steam consumption was: minimum load 20.26
pounds, maximum load 22.03 pounds, and maximum consumption
25.31 pounds. The average steam consumption for simple passen-
ger locomotives was: minimum load 18.86 pounds, maximum load
21.39 pounds, and maximum consumption 24.41 pounds. When
these figures are compared with those of the best stationary engines,
some idea of the economy of the locomotive can be obtained. The
steam consumption of an automatic, tandem-compound, condensing
stationary engine with piston valves under full load is about 18
pounds per indicated horsepower per hour, whereas the compound
non-condensing locomotive is about 21 pounds. A Corliss engine or
a medium speed, four-valve simple engine will give a minimum steam
consumption of about 22 pounds per indicated horsepower per hour
under full load. A simple freight engine under full load will use about
23.5 pounds of steam per indicated horsepower per hour. The fore-
going figures speak well in favor of the economy of a steam locomotive,
which is operated under conditions unfavorable to the securing of
good economy.
Engine Characteristics. The engines used on locomotives may
be simple or compound; in fact, both are used extensively, although
the simple type predominates. It is to be noted that the steam
locomotive is equipped with two separate and distinct engines — one
being attached to each side of the boiler, and both attached to the
driving wheels through the medium of the frames, etc.
The mechanical construction of these engines is quite similar
to that of the type already described in this work. Certain features
are made necessary in order to properly tie together the engine, boiler,
and transmission mechanism. Perhaps the most noticeable change
in detail is in the construction of the cylinders and valve seats, other-
>ise there is little variation from the well-established principles of
engine design. The valves, rods, crossheads, guides, etc., are
STEAM ENGINES 65
made of the same high-grade material and constructed in the same
first-class manner as is required for a good stationary engine. This
being true, much of the discussion of the steam stationary engine
and its parts aheady given is applicable to the engines of a loco-
motive. There are, however, many perplexing questions that arise
with reference to the performance and operation of the locomotive
as a whole that are never encountered in stationary practice, due to
the unusual and sometimes trying conditions under which the loco-
motive must be operated. The solution of these problems demands
a great amoimt of ingenuity and engineering ability.
To discuss the various types of locomotives and tell the many
interesting and important points connected therewith would require
entirely too much space, so the discussion must be confined to nar-
row limits.
Types of Locomotives. There are certain types of locomotives
common in American practice which have special names. The
eight-wheel or "American" passenger type of locomotive has four
coupled driving wheels and a four-wheeled truck in front. The
"ten-wheel" typ^ has six coupled drivers and a leading four-wheel
truck. This type is used for both freight and passenger service.
The "Mogul" type is used altogether for freight purposes; it has six
coupled drivers and a two-wheel or pony truck in front. The
"Consolidation" type is used for heavy freight service. It has eight
coupled drivers and a pony truck in front. There are also a great
many special types for special piuT)oses. In switch yards a type of
engine is used which has four or six drivers with no truck. The
Forney type has four coupled driving wheels under the engine and
a four-wheel truck carrying the water tank and fuel. This type is
used on elevated roads largely. "Decapod" engines are a type used
for heavy freight service, having ten coupled driving wheels and a
two-wheel truck in front. A tank engine is one which carries the
feed water in tanks on the engine itself instead of in the tender,
as in other engines.
A locomotive of modem design that is being largely used for
fast freight service and for heavy passenger service is illustrated in
Fig. 48. It is commonly known as the Atlantic type locomotive,
having four leading truck wheels, four coupled drivers, and a two-
wheel trailing truck. The lefwiing truck wheels ^rv^ \\\ ^ ^e»&s^s^
STEAM ENGINES
STEAM ENGINES 67
capacity. This engine is a compound type with piston valves, is
well designed, is neatly proportioned, and admirably fulfills every
requirement.
Compound Type. In connection with the subject of compound-
ing just mentioned it may be said that in recent years the compound
locomotive has been found in increased numbers on American rail-
roads. A type of compound that has given especial good service and
which is being adopted by many roads for heavy hill climbing duty
is the Mallett Articulated Compound. The adoption of the com-
pound locomotive has been due to a general opinion among railroad
officials that the findings of a conunittee of the American Master
Mechanics Association were true, as demonstrated by practice. This
Committee says of compounding:
(a) It has achieved a saving in the fuel burned, averaging 18 per cent at
reasonable boiler pressures.
(b) It has lessened the amount of water to be handled.
(c) The tender can, therefore, be reduced in size and weight.
(d) It has increased the possibilities of speed beyond sixty miles per hour,
without unduly straining the engine.
(e) It has increased the haulage power at full speed.
(f) In some classes of engines it has increased the starting power.
(g) It has lessened the valve friction per horsepower developed.
A number of other reasons are given in their report. Notwith-
standing these facts, however, the compound locomotive has not
come into very general use on railroads.
WATER PUMPS
The subject of pumping engines is a very broad one, and one
which has received the thought and study of the most eminent engi-
neers for many decades. From the earliest history of man there is
gleaned the fact that l\uman ingenuity and skill had been devoted in
those early times to the perfection of some kind of power pump.
It would be a difficult matter to mention an industry of any char-
acter or description but what a pump was needed somewhere in the
enterprise. It was first used in a large way in the mining industries
for pumping water out of the mines. Today it is found in all power
houses, mines> and factories of various kinds. Both the large and
small cities depend upon it for their water supply. The heating
and ventilating systems of modern apartmeut \vaws«5» ^\A ^^JSsRfc
68 STEAM ENGINES
buildings use the pump, and mention might be made of many other
instances where the water pump is indispensable.
There are two general classes of pumps, namely, crank or fly-
wheel type and direct acting pumps.
Crank or Hywheel Type. The crank or flywheel type was the
first form to be developed. These pumps vary greatly both in their
design and in the details of their construction. They are* of vary-
ing sizes, including some of the largest and most expensive in the
world. As a general thing they are used in heavy hydraulic enter-
prises, for furnishing water supply for cities, and in various other
enterprises where a large and constant supply of water is demanded.
In this class of pumps or engines the application of the power in the
steam cylinders in driving the pump plunger or piston varies greatly
both in design and detail of construction. Long or short beams or
bell cranks may be used and sometimes gearing may be employed,
but in all cases the limit of the stroke of the steam piston and of the
pump plunger is governed by the crank of a revolving shaft. In
pumping engines it is not absolutely necessary to have a revolving
shaft, the only requirement being that the piston in the pump cylin-
der shall be driven back and forth with a plain reciprocating motion
which may be exactly like that of the steam piston. For this reason,
in early pumping engines and also in modern engines, the reciprocat-
ing motion of the steam piston is applied directly, or through a beam,
to produce the reciprocating motion of the pump piston or plunger
without the use of any revolving part. Frequently, however, it is
desirable to use a flywheel so that the steam may be used expansively,
and in these cases, of course, a revolving shaft must be used.
Cameron BelUDriven Pump. The power pump used as an illus-
tration, Fig. 49, is a belt-driven one. The belt is placed on the pulley
1 and can be shifted to a loose pulley by the shifter 2, when desired.
The shaft 4> which is driven by the belt pulley, extends across the
frame and has attached to it a flywheel 6 and a small gear wheel,
which meshes with the large gear wheel 3. The gear wheel 3 is keyed
to the crank shaft 6, hence, when it is driven, the crank shaft is made
to revolve, which in turn gives a back and forth movement to the
piston as in the ordinary steam engine. The flywheel 5, attached
to the revolving shaft, may be of greater or less diameter and weight,
depending on the condition under which the pump is to be operate
STEAM ENGINES 69
In addition to assisting the crank to pass the dead center at each end
of the stroke of the piston, it can be employed as a reservoir in which
any excess energy may be stored at the beginning of each stroke and
drawn out during the latter part of the stroke, where the force of
the water column is greater than that of the steam. By this means
it is possible to use shorter cut-oiTs In the cylinder than could other-
wise be permitted; hence, a resulting saving in steam. Many means
may be used to drive the power pump. While the illustration shows
Bcli-DrivaD Pom
one belt driven, yet they are frequently electrically driven, and
sometimes the revolving shaft is attached to the shaft of a gas or
steam engine.
Deep-WeU or Mine Pump. For deep-well or mine pumping, the
cylinders are often set in a vertical position directly over the pump
cylinder. Ths piston rod extends from the steam cylinder directly
below to the pump plunger. Sometimes it ia possible to use steam
expan^vely in these pumps by reason of the weight of the recipro-
cating parts. When the weight is suiBdent, the steam can be cut
off before the end of the stroke and the momentum of the ijai^ -^ra.
70 STEAM ENGINES
be enough to just finish the stroke, consequently these pumps are
sometimes compounded. They are used only in pumping from very
deep wells.
Direct-Acting Type. A direct-acting steam pump is one in
which there are no revolving parts, such as shafts, cranks, and fly-
wheels, the power of the steam in the steam cylinder being transferred
to the piston or plunger in the pump in a direct line through the use
of a continuous rod or comiection. In pumps of this construction
there are no weights in the moving parts, other than those required
to produce suffident strength in such parts for the work they are
required to perform and, as there is consequently no opportunity
to store up power in one part of the stroke to be given out at another,
it Is impos^ble to cut of! the steam in the steam cylinder during any
Tig. so. Dircet-Aciinc Duplei Pump
part of its stroke. The uniform and steady action of the direct-act-
ing steam pump is dependent atone on the use of a steady uniform
pressure of steam through the entire stroke of the piston, against a
steady, uniform resbtance of water pressure In the pump; the differ-
ence between the power exerted in the steam cylinders and the resist-
ance in the pump governs the rate of speed at which the piston or
plunger of the pump will move. The length of the stroke of the steam
piston within the steam cylinders of this class of pumps is limited,
and is controlled alone by the admission, compression, and release
of the steam used in the cylinders.
Duplex Pump wiik Rocker and BeU'Crank Lecer. The direct-
acting steam pump, l^^g. 50, is known as a duplex pump and con-
sists simply of two direct-acting steam pumps placed ade by side.
The steam pistons are at one end and the water pistons at the other.
STEAM ENGINES 71
The steam pressure acts directly on the pistons; no flywheel is used;
and since the reciprocating parts are comparatively light and there
is no revolving mass to carry by the dead points, it is evident that
in the ordinary form there can be no expansion of steam. The
pump is inexpensive and g'.ves a positive action. It uses a relatively
large quantity of steam, but for small work the absolute amount is
not very great.
On the piston rod of each pump is a bell-crank lever which
operates the valve of the other pump. There must be a rocker on
one side and a bell- crank lever on the other, because of the relative
motion of the valves and pistons. The first piston, as it goes for-
ward, must use a rocker, because it draws the second valve back.
The second piston, as it goes back, must use a bell-crank lever because
it must push the first valve back in the same direction as its own
motion. The two pistons are made to work a half-stroke apart,
ttius one begins its stroke when the other is in the middle. In this
way a steady flow of water is obtained, as both pumps discharge
into the same delivery pipe. In large pumps of this kind, and even
in some small ones, the motion described above merely admits steam
to a small auxiliary piston on each steam cylinder, which then moves
the main steam valve by steam pressure.
Duplex Pump with Tappet. Some pumps operate the steam
valve by means of a tappet instead of a rocker and a bell-crank
lever, Fig. 51. Its construction and operation is as follows:
A is the steam cylinder; C, the piston; L, the steam chest; F,
the chest plimger, the right-hand end of which is shown in section;
G, the slide valve; H, a lever, by means of which the steam-chest
plunger F may be reversed by hand when expedient; // are reversing
valves; KK are the reversing valve chamber bonnets; and EE are
exhaust ports leading from the ends of the steam chest direct to the
main exhaust and closed by the reversing valves II.
The piston C is driven by steam admitted under the slide valve
G, which, as it is shifted backward and forward, alternately connects
opposite ends of the cylinder A with the live steam pipe and exhaust.
This slide valve G is shifted by the auxiliary plunger F, the latter
having hollow ends which are filled with steam, and this, issuing
through a hole in each end, fills the spaces between it and the heads
of the steam chest in which it works. Pressure being equal at ^%.^
72
STEAM ENGINES
end, this plunger F, under ordinary conditions, h balanced and
motionless; but when the mmn piston C has traveled far enough to
strike and open the reverse valve /, the steam exhausts through the
port E from behind that end of the plunger F, which immediately
shifts accordingly and carries with tt the slide valve G, thus revers-
ing the pump. No matter how fast the piston may be traveling, it
Fia, 91. SntloD of Pomp Cylinder ShoviDg Valve Opanited with Tappet
must instantly reverse on touching the valve /. In its movement
the plunger F acta as a slide valve to close the port E and is cushioned
on the confined steam between the ports and steam-chest cover.
The reverse valves II are closed as soon as the piston C leaves them
by a constant pressure of steam behind them conveyed direct from
the steam chest through the ports shown by dotted lines.
The motion of the piston C, Fig. 52, is transmitted through the
rod Ai to the water piston in the cylinder R, As the piston moves
STEAM ENGINES
73
back and forth, water enters through the intake valves and leaves
through the discbarge valves immediately above, and finally leaves
through the delivery pipe P. In order to create a more continuous
flow of water, an air chamber Q is provided. Any sudden variation
in the pressure in the line is taken up largely by the ur chamber.
It also serves to lessen the effect of water hammer.
He. 62. Section of Duplai Pump with Tappet
SPECIAL ENQINES
Under this heading may be placed a large number of engines
which have been built for a very definite field of usefulness, such as
various types of fire engines and automobile engines, where steam
b used as the motive force. Again a number of experimental engines
have been built, commonly known as freak engines, having peculiar
construction and design, which never got beyond the experimental
stage. Rotary enpnes as well as rotary pumps have been used to
some extent, but the rotary engines thus far developed have been so
extravagant in steam consumption that their use has been discon-
tinued. It b thus seen that under the head of special engines ms.o.'i
74 STEAM ENGINES
of the engines already discussed, as well as an untold number of
others of more or less merit, may be property classed.
The special engines referred to above were not mentioned for
the purpose of studying them, but rather to indicate that outside
and distinct from the steam engines classified and considered, there
are a large number of special types that should not be entirely ignored.
MARINE ENGINES
The subject of Marine Steam Engines is a broad and important
one, and to treat it properly would require one or two volumes the
size of this one. However, it seems desirable to discuss the subject
in a very general way in connection with the still broader subject of
The Steam Engine, and thus give the student a general idea of
marine engine parts.
Definition of Terms. Before taking up the subject, it is thought
advisable to present a brief statement of nautical terms used in
Starboortf
/f Fbrworg
Port
Fig. 53. Plan of Vessel Showing Different Parts
describing a vessel. Fig. 53 shows a plan of a vessel. The front part
A is called the Ixyw; the extremity B is called the stem. An object
placed near the bow is said to be forward; if near the center C, it is
amidahip; and if near the stern, it is aft An article, if placed so that
its major dimension is parallel to the line AB, is said to be placed
fore and aft Thus the crankshaft of a triple expansion engine of a
vessel b located along the line AB and is sometimes spoken of as a
fore-and-aft engine. An article located crosswise of the vessel, that
is, at right angles U} AB,i3 said to be placed aihwartship. To one
standing on the deck facing the bow, the starboard side is on his right
and the larboard, or port side, on his left.
The width of a vessel FE is its beam, and the perpendicular
STEAM ENGINES 75
distance from its lowest part to the surface of the water is called the
draft. The length of a vessel is the horizontal distance between
perpendiculars drawn at its extreme ends. The displacement of a
vessel is equal to the weight of water it displaces and is usually
expressed in long tons.
The speed of a vessel is usually expressed in knots per hour, but
is sometimes given in miles per hour. A knot is equal to about
1^ miles.
Methods of Propulsion. Speaking in a general way, the pro-
pulsion of a steam vessel is accomplished by causing a mass of water
adjacent to the ship to move in a direction opposite to that of the
ship. Motion is imparted to the water in one of the following three
ways: (1) by paddle wheels; (2) by screw propellers; and (3) by jets
of water or hydraulic propulsion.
The oldest of these three forms of propulsion, the paddle wheel,
is still much used in lake and river steamers and ferry boats; but for
ocean-going vessels and in many boats on inland waterways, the
screw propeller has supplanted it. Jet or hydraulic propulsion hi^
not proved to be practical and for this reason has never been used in
commercial work.
TYPES OF ENGINES
Beam Type. The first steam vessels were fitted with paddle
wheels, and as beam engines were the most common, this form of
engine was used. Its construction, however, was somewhat modi-
fied for this service. This arrangement of beam engine and paddle
wheel was used for many years and was appUed to ocean vessels as
well as to small river boats. It is still used, especially in this coun-
try, on river steamers and some coast steamers. The beam is sup-
ported by a large A-frame on the deck, and the engines are about on
a level with the shaft.
Engines of this type take up rather more room than those now
in common use, partly because of great size, and also because of the
shaft and paddle wheels. Another disadvantage is that in heavy
weather when one paddle wheel is thrown out of the water the other
is deeply immersed and takes all the strain, so that there is a tendency
to rack the boat. Then again if the boat is loaded heavily, the pad-
dle blades are very deeply inmiersed; while if light, they barely
76 STEAM ENGINES
touch the water. It is difficult to handle the engines satisfactorily
under either condition.
Inclined Type. The introduction of the screw propeller over-
came these difficulties very largely and at the same time required a
high speed engine. At firsts the increased speed was supplied by the
use of spur-wheel gearings but gradually higher speed engines were
built and connected directly to the propeller shaft. It was^ of course,
difficult with small width at each side of the shaft to use horizontal
engines, therefore various arrangements of inclined engines were
used before the vertical engine was finally chosen by all as the stand-
ard form for marine work. It is only in recent years that the verti-
cal engine has become general in naval work and in merchant steamers.
Vertical Type. In merchant ocean steamers the common form
has three qylinders set in line, fore and aft, above the shaft, the cranks
being set 120 degrees apart in order to give a more even tinning
moment. The three cylinders are worked triple expansion, the
valves being usually of the piston type on the high and intermediate
and double-ported slide type on the low. Sometimes piston valves
are used on all the cylinders. Plain slide valves are not suitable
for high-pressure work of any kind. While steam turbines are used
to some extent in ocean-going vessels, the majority of ships in this
service are equipped with high-speed, vertical, multicylinder engines
direct connected to the propeller shaft.
Cylinder Arrangement The different arrangement of marine
engine cylinders commonly found in service is shown in Figs. 54 to 57.
Tandem- and Cross-Compound Types. In Fig. 54, A is thfe
tandem-compound aiTangement with its single crank; B is the cross-
compound with cranks set 90° apart; and C is the three-cylinder
compound with cranks set 120° apart. In arrangement C, the high-
pressure cylinder is sometimes placed between the two low-pressure
cylinders.
Triple-Expansion Type. The cylinder arrangement. Fig. 55,
is found only on the larger vessels, and is spoken of as the triple-
expansion type. In this type there are three cylinders to each engine,
and they are called the high-, intermediate-, and low-pressure
cylinders, each succeeding one being of larger Volume than the one
preceding. Fig. 55 illustrates two arrangements of the cylinders of
L triple-expansion engines. In arrangement A the cylinders follow
STEAM ENGINES
IHf^
i\
Fie. M. Diisnmi of Tuideiii mud CrDM-Compouod Cylinder Armi(cmanM
78
STEAM ENGINES
each other in natural sequence; this requires the least length of
piping. Arrangement B is frequently used, but requires more piping
than arrangement A. Another common arrangement is to put the
high-pressure cylinder in the center of the group. In any of these
systems the cranks would be set at 120°, giving a more nearly uniform
turning movement to the shaft, since each cylinder will develop
approximately one-third the total horsepower of the engine.
Still other arrangements of the cylinders of triple-expansion
engines are found in Fig. 56. Arrangement A gives the effect of a
tandem-compound between the high- and the intermediate-pressure
cylinder and a cross-compound between these two and the low-
pressure cylinder — an arrangement which results in cranks being
set at 90° with the consequent uneven turning effect, but it is some-
times resorted to because of lack of space for all three cylinders in
line. Arrangement £ is a triple-expansion engine, having six cylin-
ders. Here the volume of one intermediate-pressure cylinder
is divided among two cylinders, and the volimie of one low-pressure
cylinder among three cylinders, Thb form is very expensive and is
not often used. The arrangement requires less floor area than would
be required for the same power in a three-cylinder engine.
Quadnfple-Erpanaion Type. The last cylinder arrangement to be
considered is found on the quadruple-expansion engine. In this type
the steam goes from the high-pressure cylinder to the first inter-
mediate, then to the second intermediate, and finally to the low-
F»«ssure cylinder. The volume of each cylinder is larger than that of
STEAM ENGINES 79
the preceding cylinder. There are many different arrangements of
cylinders possible with quadruple-expansion engines. Fig. 57 shows
the arrangement of cylinders in their natural sequence with the four
cranks set 90° apart, which gives a slightly more even turning effort
Fl(. SS. Beetion of Typical Vertio»l Marina ED(ii»
than is obtained with cranks at 120°, as in the triple^xpansion
engine.
The idea in the design of a quadniple-expahsion engine is to
produce an engine more economical in the use of steam than is
80 STEAM ENGINES
obtained in any other type. With high-pressure steam, say 200
pounds and over, it gives a better economy in the use of steam than
does the triple-expansion engine. However, the saving effected in
the use of less steam is, to a very large extent, offset by an increase
in first cost, operating cost, and general upkeep.
Comparison of Marine with Stationary Types. Fig. 22, page 29^
and Fig. 58 show cross-sectional views of marine engines. In marine
work many different designs of engines are used. These two views
are intended to present merely the general features and charac-
teristics of the marine engine. In comparison with stationary
engines attention is called to the different form of frame used, lighter
frames, different details of the connecting rod, and in the latter figure
the separate crankshaft for each cylinder and the single crosshead
guide. Also the cylinders are of complicated form and have double
walls, and the pistons are of a cup shape. These points will be
brought out more in detail in what follows.
ENGINE DETAILS
Cylinder. The general type of steam cylinder for a marine engine
consists of three distinct parts, namely, the shell, the liner, and the
cover.
Shell. In Fig. 59, the shell is the outer casting forming the out-
side cylinder wall, the lower cylinder head, and the steam ports.
As its complicated form makes the casting of the shell a difficult
matter, an iron is used that runs freely in the mould. Sometimes the
lower cylinder head is not cast integral with the shell, but is fitted to
it separately like the cover.
Liner. The liner is the plain cylindrical casting or bushing, which
forms the inner cylinder wall. Its use is made necessary because
the metal in the shell is of such composition that it will not wear well
if the piston is permitted to work directly on it. The material of the
liner is usually hard, close-grained cast iron. In some cases forged
steel is used. It is secured to the shell by bolts through a flanged end,
or by stud bolts. But one end is fastened to the shell, the other end
being left free to expand under the influence of the higher tempera-
tures to which the liner is exposed.
Cover. The cover forms the upper end of the cylinder. Usually
it is made of steel to combine lightness and strength. Sometimes the
STEAM ENGINES 81
cover is cast hollow so as to form a steam jacket for the cylinder
head, but more often it is made of a single wall of metal, reinforced by
radial ribs on the outside.
Marine Details Re-
semble Stationary. Many
of the details of marine
engines are so nearly like
those of stationary en-
gines in essential features,
and the minor points of
difTerence are so varied
that special mention of
them will not be made
here. For illustrations of
different parts, reference
may be made to the ear-
lier sections of this book.
For example, Fig, 9 shows
a typiciil marine piston
and connection to the
piston rod; Fig. 14 a
typical crosshcad and
crosshead pin; Fig. Iti a connecting rod; and Figs. 18 and 19 t>'pical
main bearings.
Crosshead Guides. A form of marine crosshead guide, diiTering
from that ordinarily used in stationary work, is shown in Fig. 60.
The crosshead used with this
guide is known as the slipper type.
It has but one bearing surface,
and this runs in the space between
SS and A. In the guide the plate
/' is bolted to the engine frame
so that it receives all the cross-
head pressure when the engine is
running ahead. For backward motion of the engine the flanges
FF are provided to receive the thrust.
Cranks. In marine work side cranks are not used. The con-
necting rod is always connected between two crank arms. Further-
f^
^
Fi«. BO. Typo of M»ti
82 STEAM ENGINES
more, each cjUnder of an engine has a separate crankshaft. These
separate shafts are bolted together by flanges, as shown in Fig. 61.
The dotted lines in this figure show how, in large shafts, the center
is sometimes made hollow. This is done to make a saving in weight
and to remove inperfect portions usually found in the center. The
n«. 01.
L of M»rine En^no Cr»i
if Buliini SecUona Togethtr
center of the ahaft is the least effective of any part of it in resisting
twisting forces, and the outside is the most effective. By using a
little larger shaft, therefore, and removing considerable metal from
around its center, a shaft of the same strength as a solid one is
obtained, with a material saving in weight. The crankshafts are
usually all made of the same size, so as to be interchangeable, and thus
require fewer parts to he kept in stock.
Bearings. The bearing, Fig. 62, while not part of the engine,
will nevertheless be discussed at this point. This is called the thrust
bearing, and is used to relieve the engine of the thrust caused by the
revolving propeller in screw-propelled vessels. The propeller shaft
STEAM ENGINES 83
is turned with the collars C as a part of it. The cast-iron box R
is secured to the frame of the vessel just aft of the main engines, and
the cap G is bolted to it, as shown. The collars C press against rings
£of gun metal or brass and transmit the propeller thrust to them, and
thence to the vessel. Rings B are split and are prevented from turn-
ing by the tongue piece F. Holes P are for lubrication and holes A
i
iRr
1
"E
1
ii^ii^
k
P
i
i
W
=-
i
—^
it""
[..■L.
1
Fig. tt3. Tjja of Thnut Bt
Ib Made for Takiug Up War
are provided for water cooling when needed. Water may also be
circulated through the base.
Fig. 62 shows the principle of the thrust bearing, but it is not
much used because no provision is made for taking up unequal wear
between the brasses. Fig. 63 shows a tj^pe of bearing in which pro-
vision is made for this feature, the wear being taken up by means of
the nuta fitted to the long screws at either side of the thrust beucv&%.
84 STEAM ENGINES
Thrust Bearing Calculations. The number of collars required
in any given thrust bearing depends primarily on the total thrust
that will come on them. There may be a large number of collars of
small diameter or a small number of large diameter. The experience
of the designer is usually the determining factor as to the number
used.
Knowing the number of collars required, their diameter may be
computed from the following formulas, in which n is number of
collars; D is diameter of collars; d is diameter of shaft; P is total
thrust; and p is safe allowable pressure per square inch of area, which
is usually taken as 60 pounds per square inch.
First taking the formula expressing the total thrust, we have
and substituting for j) the value of 00 pounds per sq. in., there results
the formula
P = 60X^{D^-(P)n
4
= 47 (D^-(P)n
Transposing in the last formula and solving for the value of Z), there
results the equation
Z) = >/
p
4/n
which gives the diameter of collars required for the conditions
assumed.
AUXILIARY APPARATUS
The auxiliary apparatus aboard a ship is far more numerous
than would be suspected by one not acquainted with it or even by
one familiar with the apparatus in stationary power plants. The
general features of some of the more important pieces of apparatus,
onlv, will be described.
Reversing Mechanism. The reversing mechanism of large
marine engines is so large and heavy and, at times, has to be moved
so quickly that it cannot be done by hand. Consequently, in some
instances a small steam power cylinder is attached to the reversing
gears to move them. This apparatus is called the steam-starting
gear and is under the control of the engineer.
STEAM ENGINES 85
The action of tiiis gear, Fig. 64, is as follows: When tiie revers-
ing lever, or handle, is moved from the mid-position A to B, the rod
CE is moved to the left. This movement raises the rod H, which is
connected to the lever fulcmmed at T. As the rod H raises, the rod
tig. H. Dttoili or Steun Starting Onr
moves downward, thus causing the arm M to move downward and
the arm N to move to the right. This movement of the arm JV and
pin / causes a corresponding movement to the right of the reach rod
and link, to which it is connected. Thus it is readily seen that the
movement of the reversing lever A moves the link slightly and a.t.^1;^
86 STEAM ENGINES
same time causes steam to be admitted to the power cylinder, which
acts on the piston and aids in the movement of the links.
Condensers. Surface Type. In marine work the surface con-
denser is used almost exclusively, because with this type the cooling
water (sea water) does not come in contact with the steam, and the
latter can then be used over and over in the boilers. Jet condensers
on ocean vessels would prevent the continued use of the condensed
steam because of the deposit the salt of the water would leave on the
boiler tubes and shell.
Keel Type, In small boats, such as steam launches, the surface
condenser would occupy much valuable room and add considerable
weight, so a substitute, called the keel condenser, is frequently used.
This consists of several rows of copper tubes placed outside the hull
along the keel of the boat. The engine exhaust enters at one end of
these tubes, is condensed by the sea water in contact with the outside
of the tubes, and is then drawn out of the condenser by the air pump
and pumped back to the boiler. This form of surface condenser
requires no circulating pump.
Pumps. Centrifugal Type, The pump most often used on
shipboard to circulate condenser cooling w^ater is of the centrifugal
type, driven by an independent engine or motor. The absence of
valves in this kind of pump is of advantage, as is also the fact that it
can be run through a greater range of speed and, consequently, give
greater volumes of water when occasion demands. Oftentimes the
piping is so arranged that these pumps can draw from the engine
room bilge and discharge without passing the sludge through the
condenser.
Air and Vacuum Types, Of the many kinds of air or vacuum
piunps used, the one shown in Fig. 65 has been chosen for description
as being a good example and one easy to understand. The operation
of the pump is as follows: The inlet E is piped to the outlet of the
condenser. On the up-stroke of the piston P, a partial vacuum is
formed below it, enabling the condensed steam and air in E to rush
through the foot valves F and into the pump cylinder B below the
piston. After reaching the upper limit of its stroke, P descends,
producing a slight pressure on the air and water entrained in the
cylinder, which closer the foot valves against the escape of the cylin-
der contents. As the piston continues, the bucket valves // in the
STEAM ENGINES
87
piston are forced open, permitting the escape of air and water to the
space above. On the next up-stroke this. air and water are forced
out of the air pump through the delivery valves A and the outlet N.
A small check valve, or pet-cock (not shown in the figure), is
usually located in the cylinder wall B just below the delivery valves.
When insufficient air comes through with the condensed steam to
properly cushion the piston on the up-stroke, this valve is opened to
provide the required air
for cushioning. This air l^ ^
does not affect the degree
of vacuum, because it is
on the discharge side of
the pump, where pressure
on the piston is imma-
terial as regards vacuum
in the condenser.
Vacuum is measured
by gages similar to those
used for measuring high
pressures, but calibrated
to read in inches of mer-
cury instead of pounds
per square inch. A col-
umn of mercury under
atmospheric pressure will
stand about 30 inches
high. Consequently,
since 30 inches of mer-
cury is equal to about 15
pounds per square inch, one inch of mercury will be equal to 15
divided by 30, or nearly one-half pound per square inch, the exact
value being 0.49 pounds per square inch. Suppose the vacuum gage
of a condenser reads 26. This means there has been a reduction of
pressure corresponding to 26 inches of mercury or 26X0.49, or 12.74
pounds per square inch. If the atmospheric pressure is 14.7 pounds
per square inch, then there remains in the condenser 14.7—12.74, or
1.96 pounds per square inch absolute pressure.
Besides the auxiliary apparatus already mentioned, there are
Fig. G5. Section of Air or Vacuum Pump
88 STEAM ENGINES
many more on large and small vessels which cannot be discussed
here, such as machines used for ventilation, forced draft, steering,
weighing anchor, operating hoists and capstans, compressed air and
refrigeration machines, and electric lighting.
PROPULSION
Process of Starting. When the engines are started and the
screws or paddle wheels of a ship begin turning, there is no apprecia-
ble motion of the ship for a short time. During this short time the
work done by the propellers is all used in overcoming the inertia of
the vessel. As the inertia is overcome, the ship gradually begins to
move and increase its speed. As the speed increases, the resistance
offered to the motion of the ship through the water also increases.
When all the power of the screws or paddle wheels is used in over-
coming the resistance of the water to the passage of the ship through
it, then the ship will be moving along at an approximately constant
speed.
Resistance Factors for Ship in Motion. In smooth, quiet water
the resistance offered to the ship's motion may be divided into three
elements, namely: (1) frictional resistance of the hull; (2) eddy-
making resistance; (3) wave-making resistance.
The most important of these is the frictional resistance, or skin
friction. The amount of this resistance depends on the area and the
length of the immersed surface of the hull, the roughness of this
surfac^e (whether covered with barnacles, sea-weed, etc.), and the
speed of the ship.
Eddy-making resistance, which is usually small, is caused by
eddy currents following just astern of the ship and by the churn of
the propellers.
Wave-making resistance is caused by the waves made at the
ship bow.
Winds and waves also offer resistance to a ship, but the amount
of resistance due to these causes is difficult to estimate.
Variations of Resistance with Speed of I 'essel. It has been shown
by experiment that for a given ship, the resistances vary almost
directly as the square of the speed, and that the power required to
overcome these resistances varies almost as the cube of the speed.
That is, if at a speed of 10 knots an hour a ship encounters a certain
STEAM ENGINES 89
resistance R and requires a certain power P, if the speed be increased
to 20 knots, the resistance will be increased to fi* and the power to P*.
Indicated Thrust
Indicated thrust is a
mathematical expression
denoting the ratio of the
total work In foot-pounds
done by the main engines
to the distance through
which this force acts. Ex-
pressed as a formula, this
ratio becomes
_ 33.000X/.J/. P.
pN
where T is indicated
thrust in pounds; I.H.P. is indicated horse-power of en^nes; p Is
pitch of screw in feet; and N is number of revolutions per minute.
2 PLA N
Since I.H.P.= — „^^^ , this formula may be reduced to the form
^
h
h
/
L,
^
f^
-^
1
■"""
T^
—
■1 —
"i
1
^i'
a
e 1* /o
Fif. aa. Curve Showii
Where P is equivalent mean effective pressure in pounds per square
inch; L is length of stroke in feet; and A is area of low-pressure
piston in square inches.
Example. What ia the indicated thnist ot b 1200 I.H.P. marine eDgine
drivbg a propeller of 20-foot pitch at 90 r.p.m.?
SOLDTION.
J. 33,000 I.H.P.
20X90
■•22,000 pounds
The indicated thrust for any given ship may be taken from a
curve, such as is shown in Fig. 66.
Economk:al %)eed. The most economical speed of a ship is that
speed at which it can travel a given distance with the least consump-
tion of fuel. At speeds either above or below this particular speed,
the fuel consumption will be increased. To determine the most
90
STEAM ENGINES
economical speed, the amount of coal used at different speeds la
determined by trial. These amounts are then plotted, as shown in
Fig. 67. As it stands, this curve shows merely the coal consumed at
different speeds, but by drawing a line from tangent to the curve,
the most economical speed is found at the point of tangency, or in
this case at N, or about 8 knots per hour. If the coal used by the
auxiliary machinery is to be considered, then OX, the amount of
this coal, is laid off as shown, and the tangent drawn from the new
origin at X. This new line, tangent at L, gives a higher speed for the
most economical one than that given for the main engines only.
PROPELLERS
Although propellers are not, strictly speaking, a part of marine
engines, yet the two are so closely related that a brief discussion
at this point seems desirable. Screw propellers only will be considered,
because they are used more extensively than any other device for
propelling vessels of various kinds.
Details of Screw Propeller. A screw propeller is a set of blades,
usually constructed of iron or bronze, which are made to revolve in
the water at the stem of the ship, by being connected to an extension
of the main engine shaft.
STEAM ENGINES
91
Small propellers are usually cast with the hub and blades in
one piece, but large ones have a central boss to which the blades are
bolted. Propellers are made of a variety of metals, including iron,
steel, bronze, and gun metal.
Blades, The general appearance of a blade may be seen from
Fig. 68. Propellers may have two, three, or four blades. In merchant
vessels the latter is most common.
Pitch. The pitch of a screw propeller
is the distance in the direction of the axis of
the screw that would be traveled by a point
on the blade during one revolution if there
were no slip. It is similar to the pitch of an
ordinary lathe feed screw, but of course is
much larger.
Diameter. The diameter of a screw
propeller is simply the diameter of a circle
described by the extreme ends of the blades.
The ratio of the diameter to the pitch of
a propeller is ordinarily from 1 to 1.1 and
up to 1 to 1 .5. Thus for a 14-foot diameter
propeller the pitch would likely be from
14X1.1 = 15 feet to 14X1.5 = 21 feet.
Propelling Action of Screw Propeller.
When a screw propeller is revolving in a
given direction (for go-ahead motion for
instance), the blades press on the water as
the threads of an ordinary screw do upon
the threads in the nut. The pressing of the
blades on the water causes the water to be
driven backward. There is, however, a
reaction caused by projecting this mass of
water sternward which results in the ahead
motion of the boat. The useful work done by the propeller is the
work which forces the water directly sternward; of course, the
movement of water in any other direction than sternward results
in a waste power.
If the screw worked in an unyielding medium, it would advance
a distance equal to its pitch at each revolution. Hence, the speed of
Fig. 68. Typical Shape of
iUei
Propeller Blade
92 STEAM ENGINES
the screw per minute is the product of the pitch and the number of
revolutions per minute.
Example. Suppose a screw is of 18-foot pitch and makes 72 revolutions
per minute. What is the speed of the screw in feet per minute and knots per
hour?
I
Solution.
18X72= 1,296 feet per minute
1,296 X 60= 77,760 feet per hour
77,760
6,080
= 12.78 knots per hour
Slip, Water is a yielding medium and for this reason the pressure
of the blades causes the water acted on to be driven back instead of
remaining firm. Then the actual speed of the ship (when referred to
the undisturbed water at a slight distance from the ship) is less than
the speed of the screw. This difference is called slip. Slip is the
difference between the speed of the screw and the speed of the ship,
relative to still water. It is expressed in feet per minute and as a per
ceLt of the speed of the screw.
ExAMPLK. A ship is movinj? at the rate of 16 knots per hour. The
screw has a pitch of 19 foct and makes 97 revolutions per minute. What
is the sHp?
Solution.
19X97=1,843 feet per minute = si>eeil of screw
16X6,080 , ^_, , ^ . ^ 1 r u-
— r = 1,621 feet per nunute = speea of ship
SUp=l,S43- 1,621 =222 feet per minute
= ~f- = .1204= 12.04 per cent
1 , o4tj
This may be expressed algebraically as follows: Let S equal speed of
screw; * equal speed of ship; and L equal slip in feet per minute.
Then
1 = 8-^
S-s
S
X 100 = slip expressed in per cent
The slip thus found is not the actual slip, but the apparent slip.
It is not the actual or real slip, because the screw does not act in still
STEAM ENGINES 93
water, but in water that has been set in motion by the screw itself or
by the hull.
While the hull moves through the water, it sets in motion the
water in contact with it, the direction being the same as that of the
ship. The water close to the ship has a greater forward velocity than
that at a distance. Since this water has a velocity a little less than
that of the ship, it soon falls behind the hull and is found at the stem.
Thus the water in which the propeller acts has a forward velocity.
Also the velocity is influenced by the waves and eddies, due to the
lines of the vessel. On account of the many conditions that make the
velocity of the wake variable, it is difiicult to calculate it.
When the propeller is considered, it is evident that the condition
of the water in which it works should be considered. Since the
velocity is difiicult to obtain, the real slip is not easily found.
WTien slip is referred to, it is generally the apparent slip that is
intended and not the real slip. The apparent slip varies from 5 to 25
per cent — 15 to 20 per cent being a fair average. The actual slip is
usually from 5 to 15 per cent greater than the apparent.
MANAQEMENT OF MARINE ENGINES
It is of great importance that the chief engineer and all of the
assistants should be familiar with the machinery of the ship. The
steam and exhaust pipes, both main and auxiliary, and the location of
the valves should be carefully traced; also the feed pipes to the
boilers, and the piping to the condensers. It is important that each
officer should know the function of every pump and the piping from
the bilges. Unless the engineer on watch is well acquainted with all
the machinery, he cannot act promptly in case of emergency, but will
be compelled to send for the chief or find someone under him who can
furnish detailed knowledge of the part in question. The promptness
and confidence with which he can act at all times depend upon his
knowledge of all the parts of the machinery.
Before Starting. Just what to do before starting depends largely
upon the prevailing conditions and the arrangement of the machinery.
In general, the following should be observed:
All gear used in port or for repairs should be stowed away and all covers
replaced. Such valves as the inlet and the outlet valves of the circulating pump
and all valves to bilge pipes should be tried and put in proper condition. The
94 STEAM ENGINES
outboard delivery valves from all pumps should receive especial attention. The
valves to jackets and the bulkhead and regulating valves should be opened and
inspected. The valves in the main steam pipe should not be closed tightly or they
will be set fast when steam enters.
The oil cups and lubricators should be examined and put in good working
order and the necessary worsteds adjusted.
The various joints should be inspected and the glands packed.
Pressure and vacuum gages should be connected and the shut-off cocks
tried.
The bright parts of the machinery that are likely to become splashed with*
water should be oiled.
Auxiliary engines should be tried by steam if possible; if not, by hand.
Such auxiliaries as the steering engine, circulating engines, and the electric-
lighting engines should receive careful attention. In all cases, the reversing
engine should be tried before using the main engines and before entering port it
should again be tried to make sure that it works properly.
The main engine should be oiled at all the rubbing and rotating parts.
An important item is the examination of the crank pits and all the working
parts. If these parts are not examined, some obstruction may prevent the engine
from starting. The main engines should be turned through at least one revolu-
tion, both ahead and astern, by hand.
In case forced draft is used with closed stokeholds, the draft gages should
be cleaned and filled with water and the air-tight doors should be examined and
rigged. The fans should be carefully oiled and adjusted.
To Start Engine. In starting an engine the engineer in charge
must use the knowledge gained from experience, as no set rules will
apply to all engines. For instance, a small single-cylinder engine is
not started in the same manner as a large triple-expansion engine.
In the following we w^ill consider the types of machinery most used —
the triple-expansion engine and surface condenser.
In general, to start an engine it is first necessary to warm the
cylinders and form a vacuum in the condenser; the engine can then
be started by admitting steam to the cylinders.
To Form Vacuum. It is usual to fit an independent circulating
pump, so the Kingston or sea-valve should be opened and the dis-
charge valve tested to see if it lifts readily. The circulating pump is
then started so that the condenser will not become heated by the
drains and exhaust steam. The auxiliary air-pumps should then be
started to keep the main and auxiliary condensers free from water and
to form a partial vacuum. If the air-pump for the main condenser
is independent, it may be started so as to form a vacuum.
To Warm the Engines. To warm the engines, all cylinder,
receiver, and steam chest drains are put in communication with the
STEAM ENGINES 95
condenser. In order to ascertain whether or not the drains are work-
ing properly, a by-pass arrangement is often fitted. This arrangement
connects the drains to the bilges. The jackets are usually trapped to
the hot well or feed tanks, but can be drained directly to the bilges.
If all the drains are in order, open slightly the throttle valve and all
valves in the main steam pipe. This will admit a little steam to the
high-pressure steam chest. Steam is also admitted to the jackets to
assist in warming the cylinders.
Now open the by-pass valves a little to admit steam to the
receivers. The steam in the receivers finds its way into the cylinders
and helps in the warming up. To warm both ends of the cylinders
move the valve gear back and forth slowly from full gear ahead to
full gear astern. The throttle may now be opened a little wider,
enough to set the engine in motion. By means of the reversing gear,
the cranks can be made to move back and forth without making a
complete revolution.
Opening the Throttle. We will £^sume that the engine is thor-
oughly warm and (as the drains are open) free from water. Steam is
in the jackets and the starting engine and starting valves ready. The
centrifugal pump is at work circulating water through the condenser
and either the auxiliary air-pump or an independent air-pump is at
work.
To start the engines, run the links into full gear ahead or astern
and open the throttle valve. In case the engines do not start, use the
by-pass or auxiliary starting valves. The engines should be started
slowly and the speed gradually increased by admitting more steam.
After the engines have made 200 revolutions or more, the drain cocks
may be closed.
Canses of Failure to Start, Marine engines may fail to start from
many causes, but if proper precautions are observed before trying to
start there should be no difficulty. Among the causes which are not
apparent from the exterior are:
The throttle valve spindle may be broken.
The high-pressure valve (if a slide valve) may be off its seat a^d
admit steam to both ends.
The engine may be gagged; that is, the throttle will supply
steam to one side of the high-pressure cylinder and the by-pass valves
admit steam to the opposite side of the intermediate or low. In this
96 STEAM ENGINES
case the engine will not move, as the pressures are equalized. In
using the by-pass valves, the valve or valves should be used which
will produce a turning moment on the shaft. Let us suppose that
both the high- and low-pressure valves cover the ports, and the inter-
mediate slide valve is in such a position that steam can enter that
cylinder. If now the throttle is opened, the engine will not start,
because both ports are closed. If the by-pass valves to both receivers
are opened, steam will be admitted to the proper side of the inter-
mediate piston. Also the steam in the low-pressure receiver will find
its way through the exhaust cavity of the low-pressure slide valve to
the other side of the intermediate cylinder. The result will be that
the engine will not start because the high and low are not available
for starting and the pressures on the intermediate piston will balance.
In this case steam should be admitted to the intermediate receiver
only. If steam is admitted to the low-pressure receiver only, it tends
to force the intermediate valve off its seat.
The opening of the wrong starting valves will frequently produce
a similar situation.
If the engine has become gagged, it should be freed from steam.
This may be done by closing the throttle and moving the link
to the opposite extreme position. The engine can then be started
in this direction and then be quickly reversed; or it may be
started in the proper direction if the mistake is not repeated.
In case the engine will not start, one of the following conditions
may be the cause:
(a) The valve stem may have become broken inside the chest or the
valve may have become loose on the stem.
(b) One of the eccentrics may be broken or slipped on the shaft.
(c) Bearings set up too tightly or too much compression on the
packing in stuffing boxes often prevent starting.
(d) The propeller may be fouled by a rope or other obstruction.
(e) The turning gear may not be disconnected; that is, the worm
may still be in gear with the worm wheel.
Adjustments After Starting. After the engine has been running
for a short time, the following adjustments should be made:
The speed of the feed pumps to maintain the proper water level
in the boilers.
The supply of circulating water to the condensing equipment.
STEAM ENGINES 97
The amount of circulating water around the main bearings should
be reduced as low as possible to relieve the work of the bilge pumps.
The pressures in the steam jackets and the valves in the drains
should be regulated.
Lubrication. The oil cups on bearings require special attention.
The caps of lubricators should be kept in place on the oil cups to
prevent dirt and water from entering. The lubricators should be
examined frequently because the pipes and passages are likely to
become clogged.
For cylinder lubricator as little oil as possible should be used, so
as to keep the boilers free from grease. The lubricators used for this
work are discussed and described in "Steam Engines", Part II.
Hot Bearings. There are many causes for hot bearings, the most
common of which is dirt. To prevent the accumulation of dirt in the
bearings, the engine room, oil cups, and pipes, should be kept clean.
Insufficient and improper lubrication will almost always cause
heating. If the oil enters at the top, where the pressure is greatest,
suitable oilways should be cut to allow the entrance of the oil.
Another method is to lead the oil to a point of low pressure.
Other causes are improper adjustment or alignment and deficient
surface. These defects lead to excessive pressure in some parts, which
causes heating.
In many large, modern engines, the main bearings have the
castings cored out so that water circulates through the bearing con-
tinuously, but does not come in contact with the rubbing surface.
In the caps there are holes to allow the hand to feel of the bearings
and to allow air to circulate. The temperature of the circulating
water and the hand test indicate the condition of the bearing.
In case a bearing tends to become too warm, the amount of
circulating water is increased. In extreme cases of heating, the
bearing may be flooded with water, thus washing out all of the dirt
and reducing the temperature. If this water douche is used, plenty
of oil should be supplied and the bearing given careful attention.
It may be necessary to slack back the nuts on the caps for a
short time, but they should be slacked but little or there will be
pounding. Sometimes the power distribution may be temporarily
altered, that is, the power given out by any one cylinder may be
decreased, and the power given out by the others increased by running
98 STEAM ENGINES
the link in or out and adjusting the expansion gear. It may even be
necessary to reduce the speed for a time, but this is not done unless
necessarv, as it causes delav.
If the bearing is discovered to be hot, the water service should
not be applied, as the sudden cooling may cause fracture. In this
case the engine should be slowed down or stopped and the bearing
cooled with oil, sulphur, or a mixture of soft soap, water, and oil.
Bearings that are lined with white metal should receive special
attention, as the white metal soon becomes plastic and melts at
about 400° F.
The water douche should be used only in extreme cases and with
caution, because it may cause fracture and is likely to corrode and
destroy the bearings. If water must be used, the parts should be
cleaned and oiled as soon as the engines stop.
Hot Rods. Piston rods and valve rods are often kept lubricated
by means of a large brush, called a swab. Frequently in starting, a
man with a swab is stationed to keep the rods cool. If these rods
become warm because of tight glands, they may be cooled by slacking
back the gland and applying water and oil by means of a swab or
syringe. If the rod is hot and water is applied, one side may lie
cooled and shortened ; the result will be a l)ent rod. Instead of using
water, the engines should be eased. If the rod cannot be felt, a few
drops of oil or water syringed on the rod will show whether or not it
is hot. If hot, the water will hiss or the oil will burn and cause
smoke.
As with bearings, piston rods that are packed with metal packing
should receive careful attention, as the packing may run and cut the
ro<ls. The principal causes for hot rods are glands too tight or not
properly packed, piston rod not in line, and insufficient lubrication.
Knocks. Bearings should be adjusted while the engines are
running. If a bearing is loose, it will knock at both ends of the
stroke. Usually knocks can be located by the sound or by the feeling.
Knocking in the cylinder may be due to a loose or broken piston ring,
piston loose on the rod, or a nut or bolt loose. If knocking occurs,
open the cylinder and jacket drains to be sure it is not due to an
accumulation of water. If the noise continues at various speeds, it
is probably due to looseness of the piston rings. If this is the casCi
the ring nmst be re-scraped and fitted.
STEAM ENGINES 99
Jackets. The pressures in the jackets should be maintained at
the desired amount. The jacket drains are led either to the condenser
or to the feed tank. If led to the feed tank, the temperature of the
feed water is then raised. The jackets should be well drained, as
water causes a crackling noise at each stroke. The remedy is to open
the drains wide and, when clear of water, regulate the drain valves
by increasing the opening.
Bilges. The bilge pumps should be at work constantly while the
vessel is steaming, so that water will not accumulate in the bilges or
crank pits. The crank pits should not be in communication with
the bilges, or the oil from the crank pits will be spread over the
bilges. If the stokehold bilges empty into the engine room bilges,
the bilge water should be strained on account of the fine coal in the
stokeholds. Strainers should be carefully attended to, as fine coal,
waste, and articles carelessly left in the bilges are likely to choke them.
It is considered good practice to pump from wells formed in the bilges
and covered with strainers.
Linking Up. When starting, the links are placed in full gear.
When running at the required speed, the engine is linked up so that
the expansive working of the steam may be utilized. The best
position of the links for a given speed is determined by experience.
Trial will show at what position the engine will run smoothly,
economically, and without too much noise. The throttle valve should
be wide open, so that steam will enter the high-pressure chest at
nearly boiler pressure. If the engine is running at reduced speed, it
is a good plan to link up the high-pressure engine by the use of the
block in the slot of the arm on the weight shaft. This will increase
the total ratio of expansion, but will not reduce the port opening of the
intermediate- and low-pressure cylinders. If there is any probability
of a change in speed, the engineer in charge should see that the start-
ing engine is warmed and drained from time to time and be sure that
it is ready for use. Grunting of the slide valves is sometimes stopped
by running the links into full gear for a short time, then adjusting
them in a slightly different position.
Marking Off Nuts. In order to have a record of adjustments
and to aid in adjusting bearings, the following marks are made. At
each corner of the hexagonal nut near the face that bears on the
washer, a number is stamped, as shown in Fig. 69. The wojsisRX \&
100
STEAM ENGINES
"FT
f'l'MMI'I'l
VT
f09 8 r 9 s^ s e f o
Fig. 69. Marking Nuts and WuHhers
prevented from moving by some device. A part of the circumference
of the washer is marked off in, say, 10 divisions about one-half inch
apart. These divisions are then sub-divided and numbered. It is
then easy to record the position of the nut by noting what number on
the washer coincided with the corner
of the nut. Thus 1 on 1^ or 2 on 8^.
Refitting Bearings. To find out
whether or not a bearing needs refit-
ting and to ascertain the amount of
play, a lead is taken. The cap is first
removed and a piece of lead wire is
laid along the journal parallel to the
axis. Some engineers place two pieces
around the journals near the ends and
others place them diagonally. The
cap is then replaced and screwed down
hard on the liners. The cap is again removed and the leads taken
out and examined. Thev should be flattened uniformly. The
thickness shows the clearance. If the marks on the nuts at which
the leads were taken are noted, they may be compared with the
marks and leads taken sometime afterward and the location and
extent of wear known.
If the leads show that the bearing needs refitting, the caps are
first removed and the journal, caps, and oilways cleaned. The
journal is then carefully calipered and, if found oval, cut, or rough,
should be filed all over until smooth and true. This process requires
considerable care and skill for the new surface must be concentric
with the axis. The filed surfaces are smoothed by an oil stone or
emery. If emery is used, care must be taken to clean all surfaces.
After the journals are in proper condition, the brasses, if used,
are fitted by filing and scraping. A little red lead smeared on the
journal will assist in the fitting. The brasses should be eased away
at the sides, as the metal at those points is of no assistance, but
increases the friction.
If the bearings are lined with white metal, they must be relined
when the white metal is worn through. To do this a mandrel of the
same size as the journal is placed in position in the bearing and the
molten metal poured in or the strips of white metal are hammered
STEAM ENGINES 101
into the recesses. The metal stands clear of the brass about } inch
when finished.
Stopping the Vessel. Before Entering Port. When near port, the
fires should be burning light, so that there will be no diflBculty in
keeping the steam pressure down. If the pressure rises when the
engines are slowed down, there may be an unnecessary waste of fresh
water on account of the blowing of the safety valve; the loss of fuel
will also be considerable.
Before entering port all the ashes should be dumped overboard
and all the water possible should be pumped out from the bilges.
The reversing and capstan engines should be warmed ready for use.
When the engines are slowed down, the water service should be shut
off and the oil supply increased to prevent rusting of the bearings
while in port. The pressures in the receivers and jackets should be
watched, as they have a tendency to rise when the engines slow down.
Adjustments After Stopping. When the engines are done with,
the valves in the main steam pipe and the jacket valves should be
closed, but not too suddenly; the steam should then be allowed to
escape from the pipe or used up by the reversing or other auxiliary
engine. All drains and receiver relief valves should then be opened,
and the steam should be shut off from the steering and reversing
engines.
The hand-turning gear may be put in gear as soon as there is no
steam left in the engine room main ste^m pipe. The engines should
now be cleaned while warm by wiping down the rods and shafting
with cotton waste and oiling the bright parts to prevent rusting.
In case the engines are stopped suddenly, notice should be
immediately given in the fire room so that the draft may be checked
and the evaporation reduced. If the water level is low, water should
be pumped into the boilers. Every precaution should be taken to
prevent an oversupply of steam, but if it is impossible to prevent the
rise of pressure, the excess of steam may be used in the evaporators,
distillers, etc., and in pumping out bilges and crank pits. The engines
should be kept warm and well drained so as not to cause delay in
starting. If the air-pump is worked by an independent engine, it
should be kept working for a time, so that the condenser will not be
flooded w^ith water and injure the air-pump. If the air-pump is
worked from the main engine, it will of course stop as soon as the
102 STEAM ENGINES
engines stop; in this case put on a feed-pump to keep the condenser
free from water. The circulating engines may be stopped soon after
the engines stop.
As in case of entering harbor, watch receiver and jacket pressures,
and stop the supply of water to bearings, etc. If there is any chance
of starting again soon, keep the reversing engine warm and well
drained.
Precautions for Long Stay in Port. If the stay in port is to be
long, the main condensers and air-pumps should be well drained and
several of the boilers may be cleaned and repaired if necessary. The
fires should be allowed to burn themselves out gradually. If the stop
is for a short time, the fires should be banked.
Emergencies. What to do in emergencies depends upon the
arrangement of the machinery. The kind and number of engines
and their arrangement and capacities of the condensers and auxiliary
machinery often determine what course to pursue in case any part
breaks or gets out of position.
Cylinder Head Broken. If a cylinder head breaks, it should be
repaired if proper means are at hand. If it cannot be repaired, the
steam port which admits steam to that end may be blocked up by
driving in plugs of soft pine and the engine run single-acting. This is
comparatively simple if the valve is a plain slide, but with a piston
valve the many ports make it more difficult. If a cylinder head of a
triple-expansion engine breaks, and one engine must run single-acting,
the expansion gear should be arranged so that the work will be
properly divided.
Fracture in the Crankshaft. What to do in this case depends upon
many conditions. If the engine is of the multicylinder type, and the
crankshaft is made in interchangeable lengths, fit the spare length
in place of the disabled one. In case no spare length is carried and
the crankshaft of the low-pressure engine is damaged slightly, change
the low-pressure length to the high-pressure engine and place the
high-pressure length in place of the low. The low-pressure length
transmits the most power. If the damage is considerable, such as
the breaking of the crankpin, the length cannot be used and the
high-pressure engine must be disconnected. If the pumps are worked
from the high-pressure crosshead, repair the broken shaft, place it
in the high-pressure engine, and block up the steam ports to the
STEAM ENGINES 103
high-pressure cylinder. The power is then developed in the inter-
mediate- and low-pressure cylinders; the amount of power trans-
mitted to the high-pressure crankshaft being just suflBcient to work
the pumps. Probably it will be necessary to run the engines slowly
because of the weak shaft.
Piston Broken. If the piston, piston rod, or valve stem become
broken and cannot be repaired, the damaged engine must be dis-:
connected and the power furnished by the others.
Air-Pump Broken, In case the air-pump breaks and cannot be
repaired, the exhaust may be carried to the deck and the engines
run non-condensing. This is a great disadvantage if the amount of
fresh water carried is slight and the ship is far from port. In case no
separate exhaust is possible, the auxiliary air-pumps may be con-
nected and the ship proceed. In most cases, however, the auxiliary
air-pumps are not of sufficient capacity to remove all of the con-
densed exhaust steam and the air; therefore, no vacuum will be
carried, but the condensation may be returned to the boilers.
Bent Piston-Rod. In the case of a small rod and a long, slight
bend, the rod may be straightened by placing it in a lathe and
applying a powerful lever. A large rod, or one with a quick bend,
should be heated to a dull red in a wood fire. The rod is then placed
in a large lathe and straightened by an hydraulic jack. In doing this
work care must be taken that the rod is not heated too hot, does not
scale, and that the points of contact are protected by copper plates.
Eccentric Broken, If the go-ahead eccentric or eccentric rod
breaks and cannot be repaired, the go-astern eccentric can be shifted
in its place. The engine will now run ahead, but cannot be reversed.
The go-astern end of the links must be kept from dropping by some
flexible support, such as a rope or chain.
Another method is to disconnect the connecting rod from the
crankpin and crosshead of the disabled engine, and block up the
steam ports so that the steam will flow to the other cylinders by the
shortest passage. The piston should be secured on the bottom of the
cylinder. The valve should be removed. After removing the
broken valve gear, the engine is ready to start. This method may be
used if the pumps are worked from the low-pressure crosshead and
the low-pressure engine is intact. If, however, the high-pressure
eccentric is broken and the pumps are worked from that crosshead,
104 STEAM ENGINES
the same method may b^ pursued as described for a fractured crank-
shaft. That is, the valve gear should be removed, the ports blocked,
and the piston, the piston rod, crosshead, and connecting rod left in
place. The moving parts of the high-pressure engine will then work
the pumps by means of the power transmitted to the high-pressure
crank. The engme must be run slowly, but can be reversed.
STEAM ENGINES
PART II
MECHANICAL AND THERMAL EFFICIENCY
The brief historical review and the study of the various types
of engines have served to unfold the degree of perfection that
has been attained in the design and details of construction of the
modem steam engine. From a mechanical standpoint, the mod-
ern engine is highly eflBcient. A mechanical eflBciency, that is,
6 rake horseoower
.r-^p ■ / , of from 85 to 95 per cent is not infrequently
indicated horsepower
obtained. An actual test of a 12-inch Xl9J-inchX 15-inch tandem-
compound Corliss engine operating non-condensing gave a mechan-
ical efficiency of 94 per cent. That is to say, if the engine was
developing 120 horsepower in the cylinders, that 112.8 horsepower
wbuld be delivered by the engine to the flywheel. In other words,
the horsepower used in overcoming the friction of the various moving
parts was only 7.2 or 6 per cent of the total horsepower developed.
Low Thermal Efficiency Inherent From the standpoint of
thermal efficiency, however, the modem engine is very inefficient,
but it is much more efficient than the older types. Even the maxi-
mum thermal efficiency obtained is only about 15 per cent, and,
under favorable conditions, this very low figure may be so reduced
that the engine is operated at a great economic loss. It is now
proposed to briefly point out some of the causes for the very low
thermal efficiency obtained and to indicate some of the means that
have been employed to increase the thermal output of the steam
engine. In order to make this study it becomes necessary to again
refer to steam and its properties. It is well known that steam
contains a great deal of heat, and that this heat can be converted
into useful work by allowing the steam to pass from the high tem-
perature of the heat generator to the lower temperature of the
refrigerator, during this change giving up heat. There are several
106 STEAM ENGINES
forms of heat engines, all of which convert the heat contained in
some substance into work. The theoretically perfect engine shall
be considered first, and after that the modifications that go to make
up the steam engine of today.
Ideal Engine. The theoretical engine. Fig. 70, is supposed
to receive heat from the generator at constant temperature Ti until
communication is interrupted at B. The working substance expands
to C without losing or gaining any heat froni external sources until
the temperature of the refrig-
erator is reached. The engine
now rejects heat at the constant
temperature T2 of the refrigera-
tor and then compresses the
working substance without loss
or gain in the quantity of heat
until the temperatiu^ of the
heat generator is reached. These
are ideal conditions and, if ful-
filled, the efficiency of the per-
fect engine will depend only on the difference between the tempera-
ture at which heat is recced and rejected or, in other words, it
depends only upon the, aifference in temperature between the gen-
erator and the refrigerator.
If Ti equals the absolute temperature of the heat received
and T2 equals the absolute temperature of the heat rejected, then
the thermal efficiency E of the engine will be represented by the
formula
Fig. 70. Theoretical Indicator Diagram
E =
Ti
Or, in other words, the efficiency equals the absolute temperature
of the heat rejected, subtracted from the absolute temperature of
the heat received, and the remainder divided by the. absolute tem-
perature of the heat received.
Example. Given an engine using steam at a 120 pounds absolute pressure,
and exhausting at atmospheric pressure. What is the thermal efficiency?
Solution. The absolute temperature corresponding to 120 pounds
pressure is S41.314-459.5, or 800.81°, and the absolute temperature of the
exhaust is 212+ 459.5, or 671.5^ Then
STEAM ENGINES 107
800.81-671.5
800,81
= .161, or 16.1 per cent
Losses in Practical Engine. In General, In actual engines
this efficiency can not be realized, because the difference between
the heat received and the heat rejected is not all converted into use-
ful work. Part of it is lost by radiation, conduction, condensation,
leakage, and imperfect action of the valves. The cylinder walls of
the theoretical engine are supposed to be made of a non-conducting
material, while in the actual engine the walls are of metal, which
admits of a ready interchange of heat between cylinder and steam.
This action of the walls can not be overcome and is so important
that a failure to consider its influence will lead to serious errors in
computations, and no design can be made intelligently if based on
the theory of the engine with non-conducting walls. In theoretical
engines steam expands without the loss of any heat, while in the
actual engine a large amount of heat is lost by radiation. There is
also a considerable loss of pressure between the boiler and the engine,
due to the resistance offered by the pipes and cylinder passages. In
a slow-speed engine with large and direct ports and valves this
trouble is reduced to a minimum. The imperfect action of the
valve gears may also be lessened with due care, but the action of
the cylinder walls still remains to be overcome.
Theoretical and Actual Card Analysis. In the theoretical card,
admission is at constant boiler pressure, cut-off is sharp, expansion
is complete — that is, expansion continues until the temperature falls
to that of the condenser and the exhaust is at condenser pressure —
and the piston always sweeps the full length of the cylinder.
In the actual engine there is a considerable loss of pressure,
between boiler and engine, and the wire drawing of the ports and
valves tends to cause a sloping steam line. Condensation at the
beginning of the stroke causes the real expansion line to fall below
the theoretical, while re-evaporation causes it to rise above the theo-
retical toward the end of expansion. In the actual engine, release
takes place before the end of the stroke, expansion is not complete,
that is, the pressure at release is above that of the condenser, and the
resistance of exhaust ports causes the back pressure to be above the
actual condenser pressure. Moreover, the piston does not sweep the
108 STEAM ENGINES
full length of the cylinder, and the clearance space must be filled with
steam, which does very little work. The theoretical and actual
cards are shown in Fig. 71.
Mechanical Losses. It has been shown that the eflSciency of
the theoretical engine is purely a thermal consideration; the efficiency
of the actual engine, however, is largely a mechanical matter. The
unit of work is the horsepower, which corresponds to the develop-
ment of 33,000 foot pounds per minute. As 778 foot pounds are
equivalent to one British Thermal Unit, 33,000 foot pounds per
minute, or one horsepower, is equivalent to 33,0004-778 or 42.42
British Thermal Units. Now if a certain engine uses 84.84 British
Fig. 71. Superposed Ideal and Actual Indicator Diagrama
Thermal Units per horsepower per minute, it is evident that its
eflSciency will only be one-half, or 50 per cent, because 42.42 is one-
half of 84.84. Hence, it may be said that the eflSciency of the actual
42 42
engine is equal to _ . . . _. _ __ . '—- — ■ r^
Bntish Thermal Units per horsepower per minute
This eflSciency is always much less than that of the perfect engine.
ANALYSIS OF LOSSES
The eflTect of some of the losses in the steam engine and the
methods for decreasing them will now be considered.
Radiation. In the first place, the metal walls of the cylinder,
being good conductors of heat, become heated by the steam within
and transmit this heat by conduction and radiation to the air or
external bodies. With the cylinder well lagged, much less heat is
lost by radiation. If the lagging were perfect and the temperature
STEAM ENGINES 109
of the cylinder remained the same as the temperature of the steam
throughout the stroke, there would be no loss by radiation, but heat
would still be lost by conduction to the different parts of the engine.
Cooling by Expansion. During expansion, the temperatiu^ and
pressure of the steam decrease as the volume increases, and the tem-
perature at exhaust is much less than the temperature at admission.
In the perfect engine, the working substance after exhaust is com-
pressed to the temperature at admission, but in the actual engine
much of this steam is lost and the compression of a part of it is
incomplete, so that its temperature is less than the temperature at
admission.
Steam Condensation and Re-Evaporation. Consider an engine
operating wdth admission at 100 pounds absolute and exhaust at
18 pounds absolute. From steam tables the temperature at admis-
sion is found to be 327.80°, and at exhaust 222.4°. The metal walls
of the cylinder, being good conductors and radiators of heat, are
cooled by the low temperature of exhaust, so that the entering steam
in passing through ports and into a cylinder is subjected to a tem-
perature of more than 100° cooler than the steam. This means that
heat must flow from the steam to the metal until both are of the
same temperature. This causes the steam to give up part of its
latent heat, and as saturated steam can not lose any of its heat
without condensation, the cylinder walls become covered with a film
of moisture, usually spoken of as initial condensation. This conden-
sation in simple unjacketed engines, working under fair conditions,
may easily be 20 per cent or more of the entering steam. The mois-
ture in the cylinder has, of course, the same temperature as the
steam; it has simply lost its heat of vaporization.
Although metal is a good conductor of heat, it can not give up
or absorb heat instantly; consequently during expansion, the tem-
perature of the steam falls more rapidly than that of the cylinder.
This allows heat to flow from the cylinder walls to the moisture on
them. As fast as the steam expands so that the pressure in the cylin-
der becomes less, this condensation will begin to evaporate. As the
pressure falls it requires less and less heat to form steam and, there-
fore, more and more of this moisture will be evaporated. At release
the pressure drops suddenly, more heat at once flows from the cylinder
walls, and re-evaporation continues throughout the exhaust. Prob-
(
no STEAM ENGINES
ably all of the water remaining in the cylinder at release is now
re-evaporated, blows out into the air of the condenser, and is lost
as far as useful work is concerned.
The steam that is first condensed in the cylinder does no work;
its heat is used to warm up the cylinder, and later, when it is re-evap-
orated, it works only during a part of the expansion and at a reduced
eflSciency, because it is re-evaporated at a pressure and, consequently,
at a temperature very much lower than that of admission. If the
cut-off is shorty perhaps 20 per cent of the steam condensed may be
re-evaporated during expansion; if the cut-off is long, 10 per cent
may be re-evaporated, the rest remaining in the cylinder at release,
still in the form of moisture. Thus some of the entering steam passes
through the cylinder as moisture imtil after cut-off, and still more
passes entirely through without doing any work.
Suppose an engine is using 30 pounds of steam per horsepower
per hour and admission is at 100 pounds absolute. The latent heat
of vaporization at this pressure is 884 British Thermal Units per
pound. If the condensation amounts to 33 J per cent, then 10 pounds
are condensed and there is lost 10 times 884, or 8,840 British Thermal
Units per hour, or 147.3 per minute; and since 42.42 British Thermal
Units represent 1 horsepower, there is lost by condensation 147.3
divided by 42.42, or 3J horsepower (nearly). If the cut-off is short-
ened, the condensation increases and may amount to 50 per cent.
Of course, very much less steam is used at a short cut-off than with
a long cut-off, and doubtless in many cases 50 per cent of the steam
at short cut-off is not as great an absolute quantity as 30 per cent at
a long cut-off.
Exhaust Waste. In addition to the actual loss from condensa-
tion in the cylinder, there is still another loss due to re-evaporation.
Suppose, as before, that 10 pounds of steam are condensed in the
cylinder, and that 20 per cent of this is re-evaporated during expan-
sion. This will leave 8 pounds to be re-evaporated during exhaust.
Suppose the exhaust is at 3 pounds above atmospheric pressure, or
18 pounds absolute (about). Then the heat of vaporization is 963.1
British Thermal Units per pound of steam, and it will require 8 times
963.1, or 7704.8 British Thermal Units, to evaporate the 8 pounds.
All of this heat is taken from, the cylinder, leaving the engine much
cooler than it would be were it not for this re-evaporation. This
STEAM ENGINES 111
gives some idea of the great amount of heat passing away at exhaust,
which is known as the exhaust waste.
Clearance. In all cylinders it is necessary to have a little space
between the cylinder cover and the piston when at the end of the
stroke. In vertical engines the space is greater at the bottom than
at the top. The volume of this space, together with the volume of
the steam ports, is called the clearance. It varies from 1 to about
15 per cent, depending upon the type and speed of the engine — the
higher the speed, the greater the clearance. This clearance space
must be filled with steam before the piston receives full pressure; and
the volume of the clearance offers additional surface for condensation.
Friction. Another important loss is that.due to friction. It is
well known that it takes considerable power to move an unloaded
engine; if fitted Tivith a plain, unbalanced slide valve, the power neces-
sary to move the valve alone is considerable. The piston is made
steam-tight by packing rings, and leakage around the piston rod is
prevented by stuflSng boxes. All these devices cause friction as
well as wear at the joints. The amount of power wasted in friction
varies greatly, depending upon the kind of valves, general work-
manship, state of repair, and lubrication.
OPERATION ECONOMIES
The foregoing discussion has served to indicate that the larger
part of the heat loss occurring in the steam engine is due to initial
condensation, exhaust waste, and clearance, although the effect of
the latter has been greatly reduced by improvement in design.
Regarding the methods devised for reducing the amount of initial
condensation, the high-speed engine has in a measure decreased this
difficulty because of the very high piston speed employed. Since
the piston speeds are high, the length of time the steam remains in
the cylinder has been greatly lessened; hence the transference of
heat is considerably reduced. The piston speed is limited, however,
by the performance of the valve gear, it being well known that the
most eflBcient valve gears are those employed on the low-speed
engines. Increased piston speed also calls for more clearance space,
hence the possible gain in economy from high piston speed is limited
by the performance of the valve gear and the clearance required
for the higher speeds.
112 STEAM ENGINES
T\u' applir'ation of the iiica of multiple exjiansioii, or compound-
ifiK, liiiH timU'jitiWy ri^rlurrerl the lf>54.se» both by lessening the amount
of rorKlirriHation and also by utilizing the re-evaporated steam and
t III? Hiviitu that h'ak.s by the piston, which in some cases may be con-
Hidcrabh?, and this im[K)rtant improvement ^ill be discussed first.
In aildition, otlu*r means have been employed for the purpose of
IncreaKing the economic performance of the steam engine, as for
iriMtjince, jfirkding, nvper heating, and the use of condensers.
MULTIPLE EXPANSION
Two (*ngin(\H may be used together on the same shaft, partly
('Xpanding the* stcani in one of the cylinders and then passing it over
to the other to finish the expansion. One advantage from this
iirrungcnicnt is that the parts can Ik; made lighter. The high-pres-
siiro (\vlindcr can In* of much less diameter than would be possible
if the entirt* expansion wert* to take pla(*i» in one cylinder. This, of
et>urst\ makes thv prt*ssurt» exert tnl on the piston nnl much less, and
the pisti>n nnl and (H»nntvting nnl can thus Ih^ nuule much lighter.
The lo\v-pr^*ssurt* eviinder must In* largiT than it otherwise would
\h\ but Its |mrts !uhh1 tiot In* nuieh heavier* Invaust^ the pressure per
snuart* inch is wKnuvs low.
This arrangiMuent gives not only the advantagt^ of lighter |iarts,
but a di^^idt^l inert^ist* of ixx^nom^v over the singltM\v Under type.
If attention is gi\en to the matter, a loss of ewnom\- \^\Mikl be
e\)H\'ttHl, Invaus^^ the stt^un is oxixv^eil to a nuioh Un^T surface
thrxMigh which to Kvm^ lu>«t, but tlu^ gain ixmu^ fr\>m ainnhor <*iv,iive
and is sulVu ient to eutin^ly ivuntei^^Iamv the effe\*t of 4 Urprr oyK
imier surfa\v^
I c** C^m«!kii$Alhmi% Wln^^n \xTy high ihvssuiv steam *:xi a k:^
rx^ti^^ ^>f ^Ajviw>ioii is u?*\i. the ditTeteiKv bet^ven the ten>:vrA^::nr
\Nf tl^-^ oe,tt^^\g *iHi \^ the c\h*iisl siei»m is grwit- Fiv iv->:3fcrxv.
>uj^\v^ >tx>AW^ 411 tt^^ |x^>,«h!s v3C*i5^^ |Wi:5>uK^ CKXrt^ the iva:x>rrc
a^nJ th*-^ c\)>AUM j>w^;:tv is i i>iiHr>ls '^c*uie \ the ^fiffewtxv in teczi-
j>i^^tv,Tr *s t*ke^\ f^^n^ sw>dini uMet i< sro.r^— 21n^\ or l.>:l.>^
\^\> vhflV^rv^vv Uvx^wies w*Hx i:V ^iwrrw* if ilae 5iw=a i< vv^oiecifed
to aKv;^: :h?ee xvvu:\H «K^v\.;^r rcrs>i::e. TSf vyr.Txirt' arxi ;vr::> oc
•,V e^V'^v *?e Avvcv: %> :Sf Vv ^Nrr,r>e»r.ire oc tl^e <xi*z25C 5C«fta
STEAM ENGINES 113
IS condensed to give up heat enough to raise the temperature of the
cyHnder to that of the entering steam. As the ratio of expansion
increases, the difference in temperature increases, and consequently
the amoxmt of steam thus condensed also increases. To keep this
initial condensation as small as possible, the range of temperature
must be limited, that is, it must not have as great a difference between
admission and exhaust. To do this the expansion of the steam
must be divided between two or more cylinders.
It will be remembered that the great trouble Watt foxmd with
Newcomen's engine was its great amount of condensation, and he
stated as the law which all engines should try to approach, that the
cylinder shovld he kept as hot as the steam which enters it. This is to
avoid condensation when steam first enters. If, instead of expand-
ing the steam in one cylinder, it be expanded partly in one and then
finished in another, it will have passed out of the first cylinder before
its temperature has dropped a great deal, and consequently the
cylinder walls will be hotter than they would have been if the expan-
sion had taken place entirely in one cylinder. This would then
reduce the amount of steam condensed. The importance of this
may not be evident at first, but it makes a great difference in the
economy of the engine. If there is less condensation, there will be
less moisture to re-evaporate, and consequently less exhaust waste,
hence there will be a saving in two ways.
Methods of Compounding. In a compound engine the steam
is first admitted to the smaller, or high-pressure, cylinder and then
exhausted into the larger, or low-pressure, cylinder.
Suppose steam at 160 pounds (gauge) pressure is admitted to a
cylinder, and the ratio of expansion is such that the steam is exhausted
at about 60 pounds (gauge) pressure; then the difference of tempera-
ture is 370.7° -307.4°, or 63.3°.
If now the steam when exhausted from the first cylinder enters
a second and is allowed to complete its expansion, so that the exhaust
pressure is about two pounds (gauge) pressure, the difference of
temperature in the cylinder will be 307.4° -218.2°, or 89.2°.
Then for the simple engine, if the exhaust pressure is two pounds
(gauge), the difference of temperature is 152.5 degrees, while in the
compound engine this difference is divided into two parts, 63.3
degrees and 89.2 degrees. The cylinder condensation for both
114 STEAM ENGINES
cylinders of the compound engine will be much less than if the total
expansion took place in a single cylinder. The cylinders should be
so proportioned that the same quantity of work may be done in each.
If there are two stages of expansion, the engine is called simply
compound; three stages, triple; and four, quadruple.
Exhaust Waste Utilized. Besides reducing the excessive conden-
sation, there is still another gain in using multiple expansion. It has
been shown how much heat is lost by the exhaust waste, which in
the simple engine blows into the air or into the condenser and is
entirely lost. In the multiple-expansion engine the exhaust and
re-evaporation from one cylinder passes into the next and does work
there; furthermore, any leakage from the high-pressure cylinder is
also allowed to do work in the low-pressure cylinder.
JACKETING
The most primitive method of effecting steam economy is by
jacketing, wliich principle Watt early recognized and adopted. This
method reduces the loss due to cyUnder condensation by supplying
heat to the steam while it is in the cylinder, that is, by surrounding
the cyUnder with an iron casting and allowing live steam to circulate
in the annular space thus formed. The cylinder covers are also
made hollow to permit a circulation of live steam. A cylinder having
the annular space A, Fig. 72, filled with steam is said to be jacketed.
A lining L is often used in jacketed cylinders.
Function of Jacket. The function of the jacket is to supply
heat to the cylinder walls to make up for that abstracted during
expansion and exhaust, so that at admission the cyUnder will be as
hot as possible. The result is, that the difference in temperature
between the cylinder walls and the entering steam is considerably
less than in engines where no jacket is used. Condensation is there-
fore reduced and, since ieat flows from the jacket to the_-cylinder
during expansion, a much larger amount of this condensation is
re-evaporated bef ore relea se and it thus has an opportunity to do
some work in the cylinder. This leaves a comparatively small
amount of exhaust waste and the heat thus abstracted is made up
from the steam in the jacket. Since a large amount of heat is given
up by the jacket steam, a good deal of it must be condensed. Thus
the question is asked : "What is the advantage of this method over
STEAM ENGINES
115
that of allowing the entering steam to supply the heat by its own con-
densation?" This question is answered briefly as follows;
The loss of heat by condensing the steam would be less if the
indde of the cylinder could be kept dry. It has been indicated how
the moisture that collects by conden sation is rg^ev apor ated during
expan^on and^hgygfjiecause the pressure falls and the cylinder
walls are hotter than the steam. This re-evaporation takes place at
the e^ieuse of the lifigt in the cylinder walls and they are t hus cooled.
It has already been shown that a great many British Thermal Units
Ftf 72 Section of BtMm Encms Cylmder Bhowinc Method of JrKketinc
are thus taken from the cylinder and thrown out at exhaust at every
stroke. Now if the in^e of the cylinder can be kept dry so that
there will be little or no re-evaporation at exhaust, it will cause a
considerable saving. The steam that condenses in the jacket does
not re-evaporate, in it; but is returned to the boiler as feed water,
10 that the only heat lost is the latent heat given up dur ing conde n-
uation. If the cylinder is heated from within, both the latent heat
given up by condensation and the latent heat required for re-evapora-
tion are lost.
In a triple-expansion engine there is one distinct advantage in
allowing condensation in the cylinder, for this moisture acts as a
lubricant, and as the heat of re-evaporation passes into the next
cylinder and there does work, there is very little loss.
116 STEAM ENGINES
Saving Due to Jacketing. It is evident that a large part of the
heat of the steam jacket flows to the cylinder during exhaust and is
thus entirely lost in the simple engine. In the triple engine, how-
ever, this heat passes into the intermediate and low^-pressure cylin-
ders; consequently we might expect a greater gain from using a
jacket on a triple engine than on a large, simple engine. The main
advantage of the jacket has been previously pointed out, and as
in all cases the gain is small, there is to be found a considerable
diversity of opinion as to its real advantages. On some -engines
there is undoubtedly little if any gain, the largest gain being in the
smaller engines of, say, 200 horsepower and under. On very small
engines, such as a 5-inch X 10-inch engine when developing only one
and one-half horsepower under light load, the gain is as much as
30 per cent. On a 10-horsepower engine the gain might be as
much as 25 per cent, while on engines of about 200 horsepower the
gain would probably be 5 to 10 per cent for simple condensing
and compound condensing, and from 10 to 15 per cent for triple
expansion. The saving on large engines of, say, 1,000 horsepower
is very small, the reason being that large engines offer less cylinder
surface per unit of volume than small ones, and hence have propor-
tionately less cylinder condensation. The very small engines, in
which the gain would be the greatest, are seldom jacketed, because
they are built for inexpensive machines and the first cost is of more
consequence than the economy of operation. Owing to the cost of
construction and the care necessary to keep jackets operative, the
use of the jacket has gradually diminished. Furthermore, the intro-
duction of the high-speed and compound engines, as well as the use
of superheated steam, has reduced the advantage of jacketing to
relative insignificance.
SUPERHEATING
General Practice. The use of superheated steam is rather a
modem practice, although for many years previous to its adoption
engineers had appreciated its value in producing steam engine econ-
omy. The reason for its delayed adoption in a practical way was
due to the mechanical difficulties met with in superheating the
steam and also to the increased cost of maintenance produced by
its use. In recent years both of the objectionable features above
mentioned have been, in a large measure, overcome, so that today
STEAM ENGINES 117
superheat is being used in a large number of power plants, and also
in steam locomotives.
Before describing a superheater, it may perhaps be well to
cleariy define what is meant by superheated steam. Water, when
confined in a vessel and heated sufficiently, turns into steam^ which,
if some water still remains, is spoken of as saturated steam. Satur-
ated steam when further heated becomes superheated steam, if it
is separated from the water. To bring about this separation, a
superheater h necessary. Superheaters vary considerably in details
of construction according to the service for which they are designed,
Fi(, 73. SecUoD of Wst«>Tube Boiler Showiim AppUcatioD of Foitci
there being, for instance, quite a difference between the superheater
designed for a stationary plant and one designed for a locomotive.
Foster Superheater. A Foster superheater as applied to a water-
tube boiler is illustrated in Fig. 73. The superheating element
is shown at B, which is connected to the steam space of the boiler by
the pipe A. The saturated steam from the boiler passes through
the pipe A, through the superheater, and then is conveyed to the
engine through the valve C. In this installation the superheater is
placed in the passage provided for the transmission gases to the
chimney, hence it is heated by what would otherwise be lost heat.
The manner of installing superheaters varies a great deal. Some are
118
STEAM ENGINES
w^m^A
entirely separated from the boiler, being self-contained and supplied
with a grate for separate firing.
The Foster superheater, Figs. 73 and 74, is made up of a num-
ber of elements placed parallel to each other, each of which consists
of two straight steel tubes, one inside of the other. The elements
are joined at one end to manifolds or connecting headers, and at the
other end to return headers for which return bends are often substi-
tuted. On the outside of the tubes B, Fig. 74, are fitted a series of
cast-iron annular flanges 2), placed close to each other and carefully
fitted to the tube so as to be practically integral with it, at the same
time exposing an external surface of cast iron, which metal is best
adapted to resist the action of the heated gases. The rings are care-
fully bored to gauge, and shrunk on the tubes. Once being in posi-
tion, the rings and tubes act vir-
tually as a unit. As the coeflS-
cient of expansion of steel is a trifle
greater than that of cast iron, the
rings grip the tubes even tighter
when in service. This form of
construction is flexible and dur-
able. It provides a section of
great strength and entire freedom
from internal strains. The mass
of metal in the tubes and covering
acts as a reservoir for heat, which
is iniparted to the steam evenly,
tending to secure a constant tem-
perature of steam, even though the temperature of the hot gases does
fluctuate. The seamless drawn tube secures great initial strength,
which is reinforced by the rings shrunk on the outside. Inside of
the elements there are placed other tubes C of wrought iron, which
are centrally supported by means of knobs or buttons regularly
spaced throughout their length. These inner tubes are closed at the
ends. A thin annular passage E from the steam is thus formed
between the inner and the outer tubes. The steam clinging closely
to the heating surface is quickly heated in the most efficient manner.
The superheater must be as free as possible from the liability
of burning out in case of a chance of overheating of the exposed
WMM
Fig. 74. Section of Foster Superheater Tubes
STEAM ENGINES
119
surfaces. The circulation must be properly distributed throughout
the superheater at full load as well as at partial loads. The various
parts must be accessible for inspection, both externally and inter-
nally, and must be readily renew able or easily repaired There must
be provision for free expansion and contraction of the vanous parts.
The supporting arrangement must be carefully lAorked out Cast
iron has given excellent results in producing durable superheaters
and has been extensively used because of its ability to withstand high
temperatures. For high steam pressures, however, cast iron is not
considered safe and has given way to the use of seamless steel tubes,
which are homogeneous and strong, but lack the heat-resisting quali-
ties of cast iron. It is evident that a combination of these two
metals will preserve the good qualities of both.
Separately-Fired Superheater. A type of superheater differ-
ing radically from the one previously described is illustrated in Fig.
75. It is a separately-fired superheater and its construction is very
120 STEAM ENGINES
similar to the Stirling water-tube boiler. The saturated steam from
the main boiler plant enters the rear superheater drum i, passe-^
through the rear bank of tubes 7 into the lower drum 2, thence to the
upper drum S, from which it passes into the pipe line through th(»
opening 4- The furnace is similar to that used in the standard
design of Stirling boiler. To protect the superheater tubes from
high temperatures of the furnace, a sufficient amount of boiler heat-
ing surface, as drums 6 and ^ and bank of tubes 9, is located in front
of the superheater proper in order to reduce the temperature of the
gases to about 1,500 degrees by the time they reach the superheater.
The builders state that when the gas temperature reaches 1,500
degrees in the standard boiler, 19 per cent of the boiler heating sur-
face has been swept over by the gases, 50 per cent of the steam pro-
duced by the boiler has been generated, and the boiler heating surface
per horsepower is 3.8 square feet. Consequently in the independently
fired superheater shown in Fig. 75, 50 per cent of the heat absorbed
is used to generate the steam, which is added to steam furnished by
the main boiler plant and hence increases the capacity of the plant in
proportion. The remaining 50 per cent of the heat, a portion of
which passes out the stack, is absorbed by the superheater and super-
heats both the steam from the main boiler plant and that from the
front bank of water tubes. The superheater, because of the front
generator set, will produce about 12 per cent of the amount of
steam furnished by the main boiler plant. As a further precaution
against any possible overheating of the superheater tubes near the
furnace, a flap valve 12 is placed in the pipe conveying saturated
steam to the superheater, as shown in Fig. 75. The spindle of this
valve is connected by links to the superheater damper IS, so that
the damper to the opening is regulated according to the quantity
of steam flowing into the superheater. If the steam flow stops, the
valve 12 drops to its seat and the damper IS is closed. Independ-
ently fired superheaters are furnished in any desired capacity, suit-
able for any degree of superheat up to about 300° F. The upper
water drum 6 and the lower superheater drum 2 are connected by
piping, hence, if desired, the superheater sections may be flooded,
converting the whole into a saturated steam boiler.
Purposes of Superheaters. These two types of superheaters
illustrated and described will suffice, and we may now direct our
STEAM ENGINES 121
attention to a study of the purposes of the superheater and to
some consideration of the economy secured by its use. The pur-
poses of superheating steam, as practiced in the past and as recog-
nized at present, are, according to Thurston, the following:
(1) Raising the temperature which constitutes the upper limit
in the operation of the heat-engine in such a manner as to increase
the thermodynamic efficiency of the working fluid.
(2) To so surcharge the steam with heat that it may surrender
as much as may be required to prevent initial condensation at
entrance into cylinder and still perform the work of expansion with-
out condensation or serious cooling of the surrounding walls of the
cylinder.
(3) To make the weight of the steam entering the condenser
and its final heat charge a minimum, with a view to the reduction
of the volume of the condensing water and of the magnitude and cost
of the air pump and condenser system to a minimum.
(4) To reduce the back pressure and thus to increase the power
developed from a given charge of steam and efficiency of the engine.
(5) To increase the efficiency of the boilers both by the reduc-
tion of the quantity of the steam demanded from the original heat-
ing surface and by increasing the area of the heating surface employed
to absorb the heat of the furnace and flue gases, and also by evading
the waste consequent upon the production of wet steam.
If the steam entering a cylinder is only superheated enough to
give dry saturated steam at cut-off, the range of temperature — ^ —
i I
of the Carnot cycle is interchanged and there is, therefore, no increase
of economy from item 1. The other four sources of economy depend
upon one fundamental fact — the poor conductivity of dry steam.
To the property of non-conductivity of heat of superheated steam
is due its great advantage. On entering a cool cylinder it slowly
gives up its heat, and if the degree of superheat is sufficient there will
be little or no initial condensation. The degree to which steam
should be superheated is still a debated point, some engineers con-
tending that only a very moderate degr*?e of superheat of about 100
degrees is sufficient, whereas others maintain that no real economy is
obtained with less than 200 degrees or over. When a high degree
of superheat was first used, difficulties were encountered such a&
122 STEAM ENGINES
the disintegration of the valves, valve seats, packing rings, and other
parts subjected to the action of the superheated steam. Lubrication
was also interfered with, since many of the oils used were not suited
for such high temperatures. All of these diflSculties no doubt account
for the one time widespread objection to high degrees of superheat,
but in recent years they have in a large measure been overcome.
The author is familiar with the performance of a simple slide valve
locomotive which has been in operation for several years under degrees
of superheat ranging from 80 degrees to 214 degrees, during whicli
time no trouble has been experienced with the valves or with the
lubrication. Many European locomotives have been satisfactorily
operated with high degrees of superheat, which insures the passage
of steam through the cylinder with but little or no condensation.
Economic Advantages. The economy obtained by the use of
superheat has been clearly demonstrated by a large number of prac-
tical tests both upon stationary engines and upon locomotives. It is
to be noted also, that about the same per cent of economy has been
obtained on the various types of engines tested, the stationary tests
corroborating the results obtained upon the locomotive and vice
versa. The various tests indicate a saving of from 12 to 15 per cent
of the amount of steam used by the engine per indicated horsepower
per hour, and a saving of coal from 20 to 25 per cent. Another very
significant thing that has been determined is that the output of
power has been increased from 20 to 30 per cent, depending upon
the conditions. These three items of saving have hastened the
installment of a large number of superheaters, so that at the present
time thousands of locomotives in Europe are equipped with super-
heaters, and in the United States and Canada over 1,500 locomo-
tives are so equipped. It seems that the railroads have been
quicker to take up the idea of installing superheaters than have other
industries, so that not nearly so many superheaters are found in
stationary service.
It is to be noted that the greatest gains from the use of super-
heaters are to be expected in the more uneconomical plants. That is,
the per cent of saving by the use of superheated steam in a simple
engine would be greater than for a compound engine, and for a com-
pound engine as compared \\ith a triple-expansion engine. Several
prominent engineers have advised the reduction of steam pressures
STEAM ENGINES 123
with a relative increase in diameter of cylinders and the use of super-
heated steam. The combination of a simple engine with low steam
pressure and superheated steam will give an increased output of
power at a small cost, a result desired by all operators.
CONDENSERS
WTien low-pressure steam is cooled, it gives up its latent heat,
that is, it changes from a vapor to a liquid, and, as a liquid occupies
much less space than an equal weight of its vapor, the changing of
the steam to water greatly reduces the pressure. Therefore, by
cooling the steam in an engine cyUnder in front of the piston, the
back pressure, or resistance, is reduced, which, in turn, reduces the
pressure necessary to push the piston through the stroke and, there-
fore, lessens the steam required to do the work. This cooling is
accomplished by some form of condenser.
Theory of Condenser Action. Back Pressure. In the ordinary
non-condensing engine, steam can not be exhausted below a pressure
of 14.7 pounds absolute, because the atmosphere exerts that amount
of pressure at the opening of the exhaust pipe. In fact, this 14.7
pounds is the theoretical limit only, and in practice the exhaust is
always a little above this because of resistance in the exhaust ports
and exhaust pipe; so that 17 or even 18 pounds absolute back pres-
sure is more nearly the conditions of actual service.
During the forward stroke, steam expands from the pressure
at admission to a much lower pressure at release; then the valve opens
for the return stroke giving full steam pressure on one side of the
piston and the pressure of exhaust on the other side, the latter act-
ing against the piston and against the force of the incoming steam.
If all of this back pressure could be removed so that there would be
a vacuum on the exhaust side of the piston, the power of the engine
would be increased by just so many pounds of mean effective pres-
sure, and in addition to this the steam could expand to a very much
lower pressure and therefore work with greater economy.
Effect of Condensation. One pound of steam at 17 pounds
absolute pressure occupies 23.38 cubic feet of space in the cylinder
of the engine, but one pound of water in the condenser occupies only
about 0.016 cubic feet, which makes the steam occupy nearly 1,462
times as much space as the water into which it condenses. If then,
STEAM ENGINES
the exhaust steam could be condensed instantly, the back pressure
would be reduced almost to zero and the engine would exhaust into
Unfortunately the mere condensation of the steam will not give
a perfect vacuum because of the air, always present in the water
which comes over from the boiler. Moreover, the condensed water
is hot, and the vapor rising from it in the condensing chamber,
together with the air and some leakage would spoil the vacuum were
M«7W BUrUT
Ttt- 76. SectioB □[
if itia Surlue Typv
it not for the air pump, which removes the air and condensed steam.
Even with the best air pump it would be impossible to maintain a
perfect vacuum, but a vacuum of 26 inches, which corresponds to
about 2 pounds absolute pressure, can readily be maintained in
good practice.
It is well known that a certain amount of heat is required to
change one pound of water at a given temperature into steam at
the same temperature; this is called the latent heat of vaporization.
If the steam condenses, it must ^ve up this latent heat. The easiest
ways of doing this are either to let the steam come in contact with
STEAM ENGINES
125
pipes through which cold water is circulated, as in a surface condenser,
or mingle with a spray of water, as in a jet condenser. These two
types will now be discussed.
Types of Condensers. Condensers may be divided into two
general classes as follows:
(1) Surface condensers in which the cooling water is separated
from the steam, usually by metallic surfaces in the form of tubes,
the cooling water circulating on one side of this surface and the steam
coming in contact with the metal on the other side.
(2) Jet condensers, including barometric condensers, siphon
Fig. 77. Diagram Showing Relation of Surftuse Condenser to the Pumps Necessary for
Propjer Operation
condensers, ejector condensers, etc., in which the cooling water
mingles with the steam to be condensed.
Surface Type. The condenser shown in section in Fig. 76 is one
form of the surface type, in which the air pump and the circulating
pump are both direct acting and both operated by the same steam
cylinder. The tool condensing water is drawn from the supply into
the circulating or water pump and is forced up through the valves
and water inlet to the condenser. It flows, as indicated by the
arrows, through the inner tubes of the lower section, then back
through the space between the inner and the outer tubes. The
water then passes upward and through the upper section, as it did
in the lower, then it passes out of the condenser through the water
outlet, taking with it the heat it has received from the steam.
126 STEAM ENGINES
The exhaust steam from the engine enters at the exhaust inlet
and comes in contact with the perforated plate, which causes it to
spread. The steam expanding in the condenser comes in contact
with the tubes, through which cool water is circulating, and con-
denses. The air pump draws the air and condensed steam out of
the condenser and thus maintains a partial vacuum. This causes
the exhaust steam in the engine cylinder to be drawn into the con-
denser, at the bottom of which it collects as it condenses and is
drawn into the air pump cylinder and discharged while heated to
the hot well of the boiler. The use of this hot water as feed water
effects a considerable saving, but the great advantage of the con-
denser is the reduction of the back pressure.
Hot water can not be used by an ordinary pump as easily as
cold water because of the pressure of the vapor which arises from
the hot water. In the condenser shown, the water and air pumps
are run by the piston in the steam cylinder. Sometimes these pumps
are connected to the main engine and receive motion from the shaft
or crosshead.
The general arrangement of the surface condenser with the
necessary pumps is shown in Fig. 77. The cooling water enters
through the pipe K and flows to the circulating pump J?, which
forces the water into the condenser through the pipe L. In case
the water enters the condenser under pressure from city mains, no
circulating pump is necessary. After flowing through the tubes it
leaves the condenser by means of the exit M and flows away. Exhaust
steam enters at jS and is condensed by coming in contact with the
cold tubes; the water (condensed steam) then falls to the bottom of
the condenser f nd flows to the air pump B by the pipe E, The air
pump removes the air, vapor, and condensed steam from the con-
denser and forces it through the pipe A^ into the hot well, from which
it goes to the boilers or to the feed tank.
Circulating Pump. The circulating pump, when separate from
the condenser, is usually of the centrifugal type. This pump con-
sists of a fan or wheel which is made up of a central web (or hub) and
arms (or vanes). The vanes are curved and as the water is drawn
in at the central part, the vanes throw it off at the circumference.
A suitable casing directs the flow. This type of pump is advanta-
geous because there are no valves to get out of order and, as the lift
STEAM ENGINES
127
is little, if any, the pump vill discharge a large volume of water in a
nearly constant stream. The circulating pump is usually so placed
that the water flows to it under a slight head. The pump is driven
by an independent engine so that the circulating water may cool
the condenser even if the main engine is not working.
Jet Type. Fig. 78 illustrates the longitudinal section of an
independent jet condenser and pump. The cold water used to con-
dense the steam enters at A, passes down the spray pipe B, and is
broken into a fine spray by means of the spray eone C. This action
insures a rapid and thorough mixing of the steam and water and
consequently a rapid condensation. The
exhaust steam enters at D with a compara-
tively high velocity, which is imparted to
the water. The whole mixture of water,
steam, and vapor passes at high velocity
through the conical chamber K to the pump
cylinder F, where it is forced into the pipe
G. The spray cone ia adjusted by means of
the stem which passes through the stuffing
l>i>x at the top of the condenser. The
valves are shown at // and K. The steam
end of the pump is at L,
In Fig. 79 a jet condenser is shown con-
nected to a stationary engine. The exhaust
pipe leads from the engine to the condenser,
Lonciladiasl Section ot Indepeodaat J«t Condenosr ud Pump
WtTER DiSTRrauTWrj
130 STEAM ENGINES
the arrows indicating the direction of the flow. Cold water enters
the condenser through the pipe shown. Part of the mixture of
exhaust steam and condensed water goes to the feed-water heater,
which is kept nearly full; the rest passes to the sewer. The heater
is placed a little above the feed pump, in order that the water may
enter the pump under a slight head. This is necessary because the
pump can not raise water which has been warmed by exhaust steam
as readily as cold water.
Barometric Condenser. A type of condenser much used with
reciprocating engines, and to a limited extent with steam turbines,
is the barometric condenser, shown in Fig. 80. This condenser is
one of the jet type. Steam enters at the point marked "exhaust
inlet" in the left-hand figure and completely fills the exhaust steam
chamber, while the condensing water enters through the injection
pipe. The water rises into a distributing tray where it is broken
up into many finely divided streams as seen in the left-hand
figure. This spray condenses the steam in the exhaust chamber
and passes down the tail pipe, carrying the condensed steam with
it to the hot well. Air entering with the exhaust steam is cooled
and collected in the air collector inside of the condensing cham-
ber. A vacuum is maintained in the upper part of the condenser
so that any air which has been collected during the process of con-
densing the steam is carried away through the pipe marked "air
pump suction". A small amount of the cooler injection water is
allowed to mix with this air so as to cool it before it passes on to
the air pumps.
Westinghonse Leblanc Condenser. With the ordinary type of
reciprocating engine, a vacuum of 26 to 27 inches is usually all
that is desired. With modern steam turbines, however, a vacuum
of 28 to 29 inches is common practice, and in many plants even
these figures are exceeded. These figures, however, cannot be
attained unless a very efficient air pump is used. The Leblanc
condenser is considered one of the most eflScient types of the many
forms of jet condensers.
Fig. 81 shows a cross section of the Leblanc jet condenser, as
manufactured by the Westinghouse Machine Company. This type
is especially used in the larger steam turbine installations. In this
condenser steam enters through the large opening E at the top.
STEAM ENGINES 131
and the cooling water through B. This water is carried all around
the circumference of the top of the condenser by the annular chamber
C and is dran'n inside the cone P through helical spray nozzles D,
by the vacuum in the condenser. Inside of the cone P the water
is intimately mixed with the steam, condenses it, and falls to the
bottom of the condenser. From here the water pumps F discharge
the water from the condenser. The air released in the condenser
by the water and condensed steam rises underneath the cone P, and
is drawn off through the pipe L by the air pump A A. Tha uaJsA,
132 . STEAM ENGINES
/ is the separate water supply for this air pump, shown more in
detail by Fig, 82, which is a cross section on .1 A.
In Fig. 82, the water entering through the center of the pump
is discharged through the orifice J into a tapering pipe, the water
being emitted in a succession of layers, as indicated at G. These
layers of water are sometimes spoken of as being water pistons.
The air coming through pipe L is caught between these layers of
water and carried to the atmosphere through the long difTuser
pipe A'.
Since the cooling water enters by virtue of the vacuum, an
accidental stopping of the pumps might cause serious trouble, due
to the water rising above the top of the condenser. To take care
of such emergencies, a very simple form of vacuum breaker is pro-
vided. In case the water rises in the condenser to an undesirable
height, the float 0, Fig. 81, opens the valve N and admits air to
enter through passage Q directly into the condensing zone. This
immediately stops the inflow of water by breaking the vacuum,
and prevents damage to the turbine.
Relative Merits of Jet and Surface Condensers. In the jet con-
denser the steam, as soon as condensed, becomes mixed with the
cooUng water, and if the latter should be unsuitable for boiler-feetl
because of scale-forming impurities, acids, salts, etc., the pure dis-
tilled water represented by the condensed steam is wasted, and if it
were necessary to purchase other water for boiler-feeding, this might
represent a considerable waste of money. On the other hand, if the
STEAM ENGINES 133
cooling water is suitable for boiler-feeding or if a fresh supply of good
water is easily obtainable, the jet condenser, because of its simplicity
and low cost, is unexcelled. Surface condensers are recommended
where the cooling water is unfitted for boiler-feed and where no
suitable and cheap supply of pure boiler-feed water is available.
Condensed steam from a surface condenser makes the best boiler-
feed water, being in fact pure distilled water entirely free from scale-
forming matter and containing a considerable amount of heat, as
compared with cold feed water. If the exhaust from reciprocating
engines is to be condensed and used as boiler-feed water, a suitable
oil separator should be interposed in the exhaust pipe between the
engine and the condenser. Another advantage of the surface con-
denser as compared with the jet condenser is that there is no dan-
ger, in case of failure of vacuum pumps, of the circulating water
backing up into the engine cylinder and wrecking the engine.
Effect of Condenser on Efficiency. It has already been stated
that there is a gain in thermal eflSciency by running an engine con-
densing, but it will be more clearly seen by considering a few figures.
The thermal efficiency may be expressed by the previously men-
tioned formula
E =
Ti
This efficiency may be increased if Ti can be made larger —
which would happen if the boiler pressure were increased — or if
T2 can be made smaller, which would result from reducing the back
pressure by condensing. If the boiler pressure is raised, both the
numerator and denominator of the fraction will increase, and the value
of the fraction will be but slightly greater. If, however, the back
pressure is reduced, the numerator Ti— T2 will be larger, while
the denominator Tx will remain the same. It is apparent that this
will cause a much greater increase in eflSciency than raising the
boiler pressure a like amount.
Suppose an engine is supplied with steam at 85.3 pounds (gauge)
pressure and it exhausts at 3.3 pounds (gauge) pressure. The abso-
lute temperature corresponding to 85.3+14.7, or 100 pounds pres-
sure, is 327.86+459.5, or 787.36 degrees, and the absolute temperature
corresponding to 3.3+14.7, or 18 pounds pressure, is 222.40+459.5, or
134 STEAM ENGINES
TABLE 1
Increase in Efficiency by Use of Condenser for Various Enc:ine8
Type of Engine
Feed Water per Indicated Horsepower
Per Cent
Qained
by
Condenser
Non-Condensing .
Condensing
Probable
Limits
Pounds
Assumed
for Com-
parison
Founds
Probable
Limit A
Pounds
Assumed
for Com-
parison
Pounds
22
20
20
18
17
Simple High Speed
Simple LfOw Speed
Compound High Speed
Compound Low Speed
Triple Exp. High Speed
Triple Exp. Low Speed
35 to2G
32 to 24
30 to 22
27 to 21
33
29
26
24
24
25 to 19
24 to 18
24 to 16
20 to 121
23 to 14
18 to 12
33
31
23
. 25
29
681.9 degrees. Then the thermal efficiency determined from the
formula becomes
Ti-Tg 787.36-681,9
Tx " 787.:3G
= .134, or 13.4 per cent
If the boiler pressure were raised to 140 pounds absolute, the
efficiency would be
J. 812.59-681.9
812.59
= .161, or 16.1 j)er cent
If instead of increasing the boiler pressure a condenser is used
and the exliaust pressure reduced to 4 ])ounds (absolute), the effi-
ciency becomes
,, 787.36-612.5 ^,^
787 30 " '^^-^ ^^ ^--^ P^^ ^'^"^
Thus it is seen that if the exhaust pressure is lowered 14 pounds
absolute there will be a greater increase in efficiency than if the
boiler pressure is raised 40 pounds.
The per cent of efficiency that is obtained by the use of a con-
denser is shown in Table I.
Cost of Cooling Water Determines Condenser Economy. \Vhile
the above figures are very encouraging, yet conditions may arise
where the per cent of gain may be materially lessened or entirely lost,
STEAM ENGINES 135
due to the cost of water. Condensing engines require from 20 to
30 pounds of cooling water to condense each pound of steam used,
depending on the necessary temperature. Thus it can be seen that
the quantity of cooling water is relatively very large, and if it is
purchased from a water company, quite an item is added to the
yearly expense account for the one item of water. If, however,
some means could be provided whereby the circulating water as it
issues from the condenser could be cooled and then used over again
in the condenser, the non-condensing engine could be run condens-
ing, thus taking advantage of all the benefits due to the use of reduced
back pressure and heating of the feed water. This has been
attempted by conducting the heated discharge water to a pond,
where it is allowed to cool to a lower temperature before being used
again. Another plan is to place in the yard or on the roof of the
building large shallow pans, m which the water is cooled by being
exposed to the atmosphere. These methods are unsatisfactory on
account of the considerable area necessary and the slow action. In
addition, they are uncertain, because they are dependent upon
atmospheric conditions.
Cooling Tower and Water Table. A more efficient and at the
same time more expensive process is to use a cooling tower or a
water table. Fig. 83 illustrates the general arrangement of a cool-
ing tower located upon the roof of a building. The discharge from
the condenser is led, as shown by the arrows, to the top of the cool-
ing tower, where it is cooled before being returned to the condenser.
This cooling is effected by distributing the water, by a system of
piping, to the upper edge of a series of mats or slats, over the surface
of which the water flows in a thin film to a reservoir which is situated
in the bottom of the coolmg tower. The mats partially interrupt
the flow and, by breaking up the water in small streams, cause new
portions to be exposed to the cooling effect of the air currents. The
water from the reservoir then flows downward through the suction
pipe and is pumped by the circulating pump through the condenser.
After passing through the condenser and absorbing heat from the
exhaust steam, it rises through the discharge pipe and commences
the circuit over again.
The tower may have several arrangements and be made of vari-
ous materials. A satisfactory form is constructed ot ^l'^ T;J^2a^Rak
136
STEAM ENGINES
within the tower, or a large number of mats of steel wire cloth gal-
vanized after weaving. The tower may be supported upon a proper
foundation or upon legs, instead of being situated on the top of a
building, as the one shown in the illustration.
To assist in the cooling of the water, the air is often made to
circulate rapidly by means of a fan, which forces the air into the
lower part of the tower and upn-ard through the mats. This fan
may be driven by an electric motor, by a line of shafting, or by a
small independent engine.
In case the fan is not used, the mats are arranged so that they
are exposed to the atmosphere. This of course necessitates the
removal of the steel casing. Usually the fanless tower must be
STEAM ENGINES 137
placed at the top of a high building or in some position where the
' currents of air can readily circulate through the mats.
With an efficient type of cooling tower, the water may be reduced
from 30 to 50 degrees, thus allowing a vacuum of from 22 to 26
inches. This will, of course, greatly increase the economy of the
plant and allow the heated feed water to be returned to the boiler.
The water table is usually made of wooden slats placed in the
ground near the plant. After trickling over the slats and becoming
cooled by the air, it collects in the bottom of the reservoir and is then
pumped into the condenser.
Amount of Cooling Water Per Pound of Steam. Besides con-
densing the steam, the injection water cools it still further, so that
more than merely the latent heat is removed from it. If exhaust
steam enters the condenser at a temperature ii, it contains a certain
amount of heat, known as total heat at temperature ti. If it is con-
densed and cooled to a temperature <2, at which it leaves the con-
denser, it then contains a certain amount of heat, known as total
heat at temperature tz.
If A represents the total heat at ti and B represents the heat
of the liquid at t^, then the heat given up by one pound of condensed
steam is equal to {A—B) British Thermal Units, provided the
exhaust that enters the condenser is dry saturated steam. If C is
the temperature of the injection or cooling water and D is the tem-
perature of the discharge water, then every pound of cooling water
absorbs approximately one British Thermal Unit for every degree
rise in the temperature, or we may say that the heat absorbed is
equal to (D— C) British Thermal Units per pound of cooling water.
Then it will take as many pounds of water W to absorb {A^B)
heat units as (Z) — C) is contained in {A—B). This may be expressed
thus - , V
(flJ-«
Therefore, W represents the number of pounds of water required
per pound of steam condensed.
Example 1. Suppose steam is expanded in an engine to 4 pounds abso-
lute pressure. If the initial temperature of the cooling water is 45 degrees,
and the condenser is of the surface type, discharging water at 120 degrees^
138 STEAM ENGINES
and the temperature of the condensed steam is 130 degrees, how many pounds
of cooling water are required per pound of steam?
Solution. By consulting the steam tables, we find the total heat of
steam at 4 pounds pressure to be 1126.5 British Thermal Units. The heat
of the liquid in the condensed steam at 130 degrees is 98.0 British Thermal
Units. Then
1126.5-98.0
Tr=
120-46
13.71 pounds
EbcAMPLE 2. Suppose steam at 6 pounds absolute pressure exhausts
into a jet condenser. The temperature of the injection water is 50 degrees
and the discharge is 120 degrees. How many pounds of water are necessary
to condense 8 pounds of steam?
Solution. In the jet condenser the temperature of the condensed steam
and the discharge water is the same. We find from the steam tables that the
total heat of steam at 6 pounds absolute is 1133.6 British Thermal Units, and
the heat of the liquid in the condensed steam at 120 degrees is 88.0 British
Thermal Units. Then as before.
^ 1133.6-88.0
^ 120-60
= 14.94
Therefore, 8 pounds of water will require 14.94X8, or 119.52 pounds.
The above calculation can not be relied upon to any great
extent for we seldom know the true condition in the condenser, and
it would be of little value to us if we did know, as the exact condi-
tion will change considerably. In practice it is customary to allow
for about twice as much water as the above calculation would require.
These figures give us a fair idea of the necessary sizes of the pipes
and passages leading to the condenser, and give a basis for estimating
the dimensions of the air pump.
Coolins; Surface in Surface Condensers. The amount of sur-
face required to condense the steam in surface condensers depends
upon the conductivity of the metal, the condition of the tubes and
their thickness, and the difference in temperature between the two
sides. The tubes of a condenser are much thinner than boiler tubes,
hence we might expect them to be more efficient in condensing the
steam than the boiler tubes are in evaporating water. It has been
found in actual practice, that a surface condenser receiving cooling
water at 60 degrees and discharging it at 120 degrees will condense
from 10 to 20 pounds of steam per square foot of the tube surface per
hour. An average of 13 pounds per square foot of surface per hour
STEAM ENGINES 139
is considered a fair one. With exhaust pressure from 6 to 30 pounds
absolute, it has been found that an allowance of 1.5 to 3.0 square
feet of cooling siu^ace per indicated horsepower is sufficient, when
the initial temperatiu^ of cooling water is 60 degrees and the final
temperature is 120 degrees.
It is evident that the amount of surface will depend upon the
quantity of steam used per hour by the engine, the pressure and
temperature of the exhaust, and the temperature of the cooling
water and discharge. There must also be an allowance for ineffi-
cient work after the condenser has become fouled with service. All
these conditions make the problem so uncertain that calculations
by means of formulas are likely to be untrustworthy, and it is best
at all times to make estimates from the figures given for similar
conditions in actual service.
Feed Water Heaters. In many places where water is expensive
and the condensing engines can not be run economically, a very
considerable saving can be effected either by allowing the exhaust
steam to condense into a feed water heater, thus saving the heat
that would otherwise be wasted, or by using the exhaust steam for
heating purposes. Of course in such cases the steam consumption
of the engine is high, but if proper allowance is made for the heat
used for other purposes, the actual fuel consumpition rightfully
charged to the engine is not excessive. If the feed water is heated
by waste gases, then the gain belongs to the boiler and not to the
engine.
ANALYSIS OF ENGINE MECHANISMS
CRANK EFFORT
In the steam engine the steam exerts a pressure on the crank
pin through the piston rod and connecting rod. When the crank is
at the dead center, the entire pressure is on the bearing of the crank
shaft, and there is no tendency to turn the crank. As the crank pin
moves from the dead center, the tendency increases until it reaches
a maximum and then decreases until, at the other dead center, it is
zero again. If the connecting rod were of infinite length and steam
were admitted throughout the whole stroke, the maximum tendency,
or the maximum turning moment as it is called, would occur with
the crank at right angles to the line connecting the dead points.
140 STEAM ENGINES
Variable Thrust. In the actual engine the thrust along the
rod is constantly varying even though the pressiu^ on the piston
remains the same. This is due to the angularity of the connecting
rod. The turning moment is always equal to the thrust along the
connecting rod multiplied by the perpendicular distance from the
connecting rod to the center of the shaft. If the steam pressure on
the piston remains constant, the maximum turning moment occurs
when the connecting rod is at right angles to the crank, for in this
position the perpendicular distance from the rod to the center of the
shaft is a maximum and equal to the length of the crank; and, as
the rod makes its greatest angle with the line connecting the dead
center at this point, the thrust along it will also be a maximum. If
the cut-off is very early, one-quarter stroke for instance, the maxi-
mum thrust along the rod will occur earlier than at the point pre-
viously mentioned, but the leverage of the force will be less, so that
really there will be little change in the point of maximum turning
moment no matter where the cut-off may occur.
Diagrams. To represent this turning moment, diagrams of
crank effort may be drawn, with rectangular co-ordinates, having
the crank angles represented as abscissas and the turning moments
corresponding to these angles as ordinates.
FLYWHEEL
Besides the thrust of the connecting rod there must be taken
into account friction and the inertia of the reciprocating parts. At
first this may be thought of small consequence but with a fairly
heavy piston and connecting rod it is obvious that at high speed the
momentum would be great. In the case of a vertical engine, on
the up stroke the steam must lift this heavy mass and impart a very
considerable velocity to it, while on the down stroke the acceleration
of the mass is added to the steam pressure. This makes the effective
force on the up stroke less than that due to the actual steam pres-
sure, and greater on the down stroke.
Function. In the case of a horizontal engine it is evident that
while the piston can push the crank around during part of the stroke,
and pull it along during another part, yet at the end of the stroke
the pressure on the piston, no matter how great, can exert no turn-
ing moment on the shaft. Therefore, if some means is not pro-
STEAM ENGINES
141
vided for making the shaft turn past these points without the assist-
ance of the piston, it may stop. This means is provided in the
flywheel which is merely a heavy wheel placed on the main shaft.
On account of the momentum of the flywheel it can not be stopped
quickly and therefore carries the shaft around until the piston can
again either push or pull.
Size of Wheel. If a long period be considered, the mean effort
and the mean resistance must be equal; but during this period there
are temporary changes of effort, the excesses causing increase of
speed. To moderate these fluctuations several methods are employed.
The turning moment on the shaft of a smgle cylinder engine
varies, firsty because of the change in steam pressiu^, and second^ on
account of the angularity of the connecting rod. Before the piston
reaches mid-stroke the turning moment is a maximum, as shown by
Fig. 84. Graphical Representation of Turning Moment of Crank Shaft of a Single-
Cylinder Engine for One Stroke
the curve, Fig. 84. Near the ends of the stroke the turning moment
diminishes and finally becomes zero. This, of course, tends to cause
a corresponding change in the speed of rotation of the shaft. In
order to have this speed as nearly constant as possible and to give
a greater uniformity of driving power, the engine may be run at high
speed. By this means the inertia of the revolving parts, such as
the connecting rod and crank, causes less variation. When the work
to be done is steady and always in the same direction, a heavy fly-
wheel may be used. The heavier the flywheel, the steadier will
be the motion. It is desirable, of course, in all engines to have steady
motion, but in some cases it is more important than in others. For
instance, in electric lighting plants it is necessary that the machinery
shall move with almost perfect steadiness. It is undesirable to use
larger wheels than are absolutely necessary, because of the cost of
the metal, the weight on the bearings, and the danger from buratix\s(,.
142 STEAM ENGINES
Methods of Reducing Size. If the turning moment which is
exerted on the shaft from the piston could be made more regular
and if dead points could be avoided, it would be possible to get a
steadier motion with a much smaller flywheel.
If the engine must be stopped and reversed frequently, two or
more cylinders are used, being connected to the same shaft. The
cranks are placed at such angles that when one is exerting its miiu-
mum rotative effort, the other is exerting its maximum, or when one
is at a dead center, the other is exerting its greatest effort. These
cylinders may be identically the same in dimension as is the case
with most hoisting engines and with many locomotives; or the engine
may be compound or triple expansion. This arrangement is also
used on engines for mines, collieries, and for hoisting of any sort
where ease of stopping, starting, and reversing are prerequisites.
Simple expansion engines wdth their cranks at right angles are usually
spoken of as being coupled.
The governor adjusts the power of the engine to any large varia-
tion of the resistance. The flywheel has a duty to perform which
is similar to that of the governor. It is designed to adjust the effort
of the engine to sudden changes of the load w^hich may occur during
a single stroke. It also equalizes the variation in rotative effort on
the crank pin. The flywheel absorbs energy while the turning
moment is in excess of the resistance, and restores it while the crank
is at or near the dead points. During these periods the resistance b
in excess of the power.
Action of Flywheel. The action of the flywheel may be repre-
sented as in Figs. 84 and 85. I^ wull be noticed that in Figi 84, the
curve of the crank effort runs below the axis toward the end of the
stroke. This is because the compression is greater than the pressure
near the end of expansion, and produces a resultant pressure on the
piston. In Fig. 85 the effect of compression has been neglected.
Let us suppose that the resistance, or load, is uniform. In Fig. 84,
the line A B is the length of the semi-circumference of the crank pin.
or the circumferential distance the crank pin moves during one
stroke. The curve A M D B is the curve of turning moment for
one stroke. M N is the mean ordinate and, therefore, A E F B
represents the constant resistance. The effort and resistance must
be equal if the speed is uniform; hence the area A E F B equals
STEAM ENGINES - 143
AM DO B. Then area A E M plus area OF B equals area MDO.
At A the rotative effort is zero because the crank pin is at the dead
point and from A to N, the turning moment is less than the resist-
ance. At N the resistance and the effort are equal. From N to P
the effort is in excess of the resistance. At P the effort and the
resistance are again equal. From P to B the resistance is greater
than the effort. In other words, from ^ to iV the work done by
the steam is less than the resistance. This shows that the work rep-
resented by the area A EM must have been done by the moving
parts of the engine. From N to P the work done by the steam is
greater than the resistance, and the excess of energy is absorbed by
or stored in the moving parts. From P to the end of the stroke the
work represented by the area F B is done on the crank pin by the
moving parts.
Fig. 85. Siraulianeous Crank Effort Curver^ of Two Engines Acting at Right
Angles to Each Other
It is known that energy is proportional to the square of the
velocity from the formula
29
in which E is energy in foot pounds, W is weight in pounds, V is
velocity in feet per second, and g is acceleration of gravity in feet per
second^. Hence as W and g remain the same, the velocity must be
reduced when the mo\'ing parts are giving out energy and increa^
when receiving energy. Thus it is seen that the action of the crank
pin is to move slowly, then more rapidly. The weight of the
revolving parts of an engine is not sufficient to absorb sufficient sur-
plus energy, hence a heavy fl^'wheel is used.
In case there are two engines at right angles, two crank effort
curves may be drawn, as shown in Fig. 85. The mean ordinate A E
is equal to the mean or constant resistance. There are two minimum
and two maximum velocities in one stroke. The diagram. sJia^'**
144 STEAM ENGINES
that the variation is much less than for a single cylinder, hence a
lighter wheel may be used.
Calcidations of Mass. The weight of the flywheel depends upon
the character of the work done. For pumping engines and ordinary
machine work the effort need not be as constant as for electric light-
ing. In determining the proper weight of a flywheel the diameter
of the wheel must be known. If the wheel is too large, the high linear
velocity of the rim will cause too great a centrifugal force and the
wheel will not be safe. In practice, about 6,000 feet per minute is
taken as the maximum linear velocity of cast-iron wheels. When
made of wood and carefully put together the velocity may be taken
as 7,000 to 7,500 feet per minute.
The linear velocity of a wheel is expressed in feet per minute
by the formula V=27z R N, or tt D N,in which V is velocity in feet
per second, R is radius of wheel in feet, D is diameter of wheel in
feet, and N is revolutions per minute.
Then if a wheel nms at 100 revolutions per minute, the allow-
able diameter would be obtained from the equation
6000 = 3.1416XZ)X100
Therefore
6000
"" 3.1416X100
= 19.1 feet
If a wheel is 12 feet in diameter the allowable speed is found to be
V
N^-
TlD
6000
3.1416X12
= 159 revolutions per minute
It is usual to make the diameter less than the calculated diameter.
Having determined the diameter, the weight may be calculated
by several methods. There are many formulas to obtain this result
given by various authorities, one formula being
in which W is weight of rim in pounds; d is diameter of cylinder in
inches; b is length of stroke in inches; D is diameter of flywheel in
STEAM ENGINES 145
feet; N is number of revolutions per minute; and C is a constant
having a value which varies for different types of engines and
for different conditions as follows:
Slide valve engines, ordinary work C= 350,'000
Corliss engines, ordinary work C « 700,000
Slide-valve engines, e/ectric lighting C= 700,000
Automatic high speed engines C — 1,000,000
Corliss engines, electric Jigh ting C « 1,000,000
Example 1. Find the weight of a flywheel rim for an automatic high
speed engine used for electric lighting. The cylinder is 24 inches in diameter;
the stroke is 2 feet. It runs at 300 revolutions per minute, and the flywheel
is to be 6 feet in diameter.
Solution.
1000000 X(24)«X 24
36X90000
»4266 pounds
Example 2. A plain slide valve engine for electric lighting is 20 inches
X 24 inches. It runs at 150 revolutions per minute. The flywheel is to be
8 feet in diameter. What is the weight of its rim?
Solution. 700000X400X24
64X22500
=4666 pounds
The weight of a flywheel is considered as being in the rim. The
weight of the hub and arms is simply extra weight. Then, if the
weight of the rim and its diameter be known, the width of the face
and thickness of the rim can be found. Assume the given diameter
to be the mean of the diameter of the inside and outside of the rim.
Let b equal width of face in inches; i equal thickness of rim in inches;
d equal diameter of flywheel in inches; and .2607 equal weight of 1
cubic inch of cast iron. Then
W==. 2607 XbXtXnd
= bXtX.8l9d
Example 3. Suppose the rim of a flywheel weighs 6,000 pounds, is 9
feet in diameter, and the width of the face is 24 inches. What is the thickness
of the rim?
Solution. yn^
'".819 d6
6000
"".819X108X24
=2.83 inches
In this case the rim would probably be made 2^ inches thick. The total
weight, including hub and arms, would probably be aboviit %^<yy^ ^^n^tn.^.
146 STEAM ENGINES
QOVBRNOR
The load on an engine is never constant, although there are
cases where it is nearly uniform. While the engine is running at
constant speed, the resistance at the flywheel rim is equal to the
work done by the steam, disregarding friction. If the load on the
engine is wholly or partially removed and the supply of steam con-
tinues undiminished, the force exerted by the steam will be in excess
of the resistance. Work is equal to force multiplied by distance;
hence, with constant effort, if the resistance is diminished, the dis-
tance must be increased. In other words, the speed of the engine
wiU be increased, and the engine will "race." Also, if the load
increases and the steam supply remains constant, the engine will
"slow down."
It is evident, then, that if the speed is to be kept constant
some means must be provided so that the steam supply shall at all
times be exactly proportional to the load. This is accomplished by
means of a governor.
Methods of Action. Steam-engine governors act in one of two
ways (1) they may regulate the pressure of steam admitted to the
steam chest, or (2) they may adjust the speed by altering the amount
of steam admitted. Those which act in the first way are called
throttling governors, because they throttle the steam in the main
steam pipe. Those of the latter class are called automatic cut-off
governors, since they automatically regulate the point of cut-off.
Theoretically, the method of governing by throttling the steam
causes a loss in efficiency, but the throttling superheats the steam,
thus reducing cylinder condensation. By the second method the
loss in efficiency is very slight, unless the ratio of expansion is already
great, in which case shortening the cut-off causes an increasing
cylinder condensation.
Control by Centrifugal Force, In most governors of the throt-
tling t>T)e and those applied to Corliss engines, centrifugal force
counteracted by some other force is employed. A pair of heavy
masses (usually iron balls or weights) are made to revolve about a
spindle, which is driven by the engine. When the speed increases,
the centrifugal force increases and the balls tend to fly outward,
that is, they revolve in a larger circle. The controlling force, which
is usually gra\'ity or springs, is no longer able to keep the balls in
STEAM ENGINES 147
their former path. When, therefore, the increase is sufficiently
great, the balls in moving outward act on the regulator, which may
throttle the steam or cause cut-off to occur earlier.
With the throttling governor, a balanced throttle valve is placed
in the mam steam pipe leading to the valve chest. If the engine
runs faster than the desired speed, the balls are forced to revolve at
a higher speed. The increase in centrifugal force will cause them to
revolve in a larger circle and in a higher plane. By means of levers
and gears, the spindle may be forced downward, thus partially clos-
ing the valve. The engine, therefore, takes the steam at a low
pressure, and consequently the speed falls slightly.
Similarly, if the load is increased, the engine slows down, caus-
ing the balls to drop and open the valve more widely; steam at
higher pressure is then admitted and the speed is increased to the
regular number of revolutions.
With the Corliss or other four-valve engines, the governor acts
differently. Instead of throttling the steam in the steam pipe,
the governor is connected to the releasing gear by rods. An increase
of speed causes the releasing gear to unhook the disengaging link
earlier in the stroke. This causes earlier cut-off, which of course
decreases the power and speed, since the amount of steam admitted
is less. If for any reason the load increases, the governor causes
the valves to be held open longer. The cut-off, therefore, occurs
later in the stroke.
Pendulum Qovemor. One of the most common forms of gov-
ernor is similar to that invented by James Watt. It is called from
its appearance the pendulum governor and is illustrated in principle
in Fig. 86. To consider the theory of the pendulum governor, the
masses of the balls are assumed to be concentrated at their centers
and the rods are made of some material having no weight.
When the governor is revolving about its axis at a constant
speed, the balls revolve in a circle having a radius r. The distance
from this plane to the intersection of the rods, or the rods produced,
is called the height and is equal to h.
If the balls revolve faster, the centrifugal force increases, r
becomes greater, and h diminishes. The mathematical expression
for centrifugal force is Wv^
148
STEAM ENGINES
in which F is force in pounds; W is weight of one ball in pounds: v is
velocity in feet per second; g is acceleration due to gravity; and r is
radius in feet. From the above equation it is seen that force varies
inversely as the radius.
While the pendulum is revolving, centrifugal force acts hori-
zontally outward and tends to make the balls fly from the center;
and the action of gravity tends to make the balls drop downward. In
order that the balls shall revolve at a certain height, the moments
of these two forces about the point of suspension must be equal, or
Fig. 86. Diagrams Showing Action of Pendulum Governor
the weight of the balls multiplied by their distance from the center
must equal the centrifugal force multiplied by the height, or
from which
WXT^Fxh
T '^ F
Substituting value of F just given, we have
h W^
r ~W^
Therefore,
h=
9^
V'
Now since v, the linear velocity of a point revolving in the circum-
ference of a circle, is expressed as 2 t r N' feet per second, where N'
STEAM ENGINES 149
is revolutions per second, this value may be substituted in the
above formula, giving
4;rV(iV7
9
and since the values of g and n are known, the formula maybe
written
32.16
4X3.1416'X(iV0«
.8146
— ,,, feet
9.775 . ^
= -—--- inches
{Ny
If it is desired to use N, the r.p.m., instead of N\ the r.p.s., the
former may be substituted in the formula by multiplying the fraction
by 60^, or 3600, giving
^ 2932.56 ^
h = — feet
35190.7 . ^
= — — mches
From the above formula it is evident that the height is inde-
pendent of the weight of the balls or the length of the rod, depending
entirely upon the number of revolutions. The height varies inversely
as the square of the number of revolutions.
The ordinary pendulum governor is not isochronous, that is,
it does not revolve at a uniform speed in all positions, the speed
changing as the angle between the arms and spindle changes.
Fly-Ball Qovemor. The early form consisted of two heavy
balls suspended by links from a pin connection in a vertical spindle,
as shown in Figs. 87 and 88. The spindle is caused to revolve by
belting or gearing from the main shaft, so that as the speed increases,
centrifugal force causes the balls to revolve in a circle of laxsj^^ \flc>^
150
STEAM ENGINES
larger diameter. The change of position of these balb can be made
to affect the controlling valves so that the admission or throttling
will vary with their position. With this governor it is evident that
for a given speed of the engine there is but one possible position for
the governor, consequently one definite amount of throttling or one
point of cut-off, as the case may be. If the load varies, the speed of
the engine will change. This causes the position of the governor balb
to be changed slightly, thus altering the pressure. But in order that
the pressure or cut-off shall remain changed, the governor balls must
stay in their new position. That is to say, the speed of the engine
Imple Tyjw of Fly.
II Oovcfnor
must be slightly changed. Thus with the old ball governors there
was a slightly different speed for each load. This condition has been
greatly improved by various modifications until now such governors
give excellent regulation.
While the engine is running with a light load, the valve con-
trolled by the governor will be open just enough to admit steam at
a pressure that will keep the engine running at a given speed. Now
if the engine is heavily loaded, the throttle valve must be wide open.
The change of opening is obtained by a variation in the height of the
governor, which ia caused by a change of speed. Thus it is seen that
the governor can control the speed only within certain limits which
are not far apart. The difference in the extreme heights of the gov-
ernor must be sufficient to open the throttle its entire range. In
STEAM ENGINES
TABLE II
Heights of Qovernor for Different Speeds of Engine
151
___ «
dumber of Revolutions
Per Minute
Height in Inches
Variation of Height in
Inches 4 Per Cent
250
.563
.0225
200
.879
.035
175
1.149
.046
150
1.564
.062
125
2.252
.090
100
3.519
.140
75
6.256
.250
50
14.076
.563
most well-designed engines, equipped with a throttling governor,
the speed will not vary more than 4 per cent, that is, 2 per cent above
or below the mean speed.
From the formula A= *—^, the heights corresponding to
given speeds can be computed as shown in the second column of
Table II. The third column is the variation in height for a speed
variation of 4 per cent or 2 per cent either above or below the
mean.
Disadvantage of Ordinary Fly-Ball Type, From Table II it
will be seen that for a considerable variation of speed there is but
slight variation in the height of the governor, this being too small to
control the cut-ofT or throttling mechanism throughout the entire
range. Also for high speeds the height of the governor is so small
that it would be difficult to construct it.
Other disadvantages of the fly-ball governor are as follows:
It is apparent that the valves must be controlled by the weight of
the governor balls. In large engines this requires very heavy balls
in order to quickly overcome the resistance of the valves. But these
large balls have considerable inertia and will therefore be reluctant
to change their speed with that of the engine. The increased weight
will also increase the friction in the governor joints and the cramp-
ing action existing when the balls are driven by the spindle will
increase this friction much further. All these things tend to delay
the action of the governor, so that in all large engines the olA-<a^o>=-
152
STEAM ENGINES
ioned governor became sluggish. The balls had to turn slowly
because they were so heavy; this was especially troublesome in high-
speed engines.
Porter Improved Type, To remedy these defects the weighted
or Porter governor, Fig. 89. was designed. It has a greater height
for a given speed, and the variation in height for a given variation
of speed is greater and, consequently, more sensitive. By increas-
ing this variation in height, the sensitiveness is increased. Thus, if
a governor running at 50 revolutions has a variation in height of .57
inch, it is not as sensitive as one having a variation of 1 inch for
the same speed.
In the weighted governor, the weight is formed so that the center
of gravity is in the axis. It is placed on the spindle and is free to
revolve. The weight adds to the weight
of the balls, and thus increases the mo-
ment of the weight. It does not, how-
ever, add to the centrifugal force, and
hence the moment of this force is un-
changed. It may then be said that the
weight adds effect to the weight of the
governor balls but not to the centrifugal
force, and as a consequence the height of
the governor for a given speed is in-
creased. If W equals the weight of the
ball as before, and W equals one-half the
added weight, the equated moments are
(W+W) r =Fh
Substituting for F its value obtained from the formula, p. 147, we have
(WV\
Fig. 89. Porter Improved Type
of Fly-Ball Governor
(
w
X
ii7:^{Ny
)
STEAM ENGINES
Since it is Icnown tliat
g .8146
4»'(ff')'~(A").'
/ ir+iy \ .8146
Hence the height of a weighted governor ia equal to the height of
1 »mple pendulum governor multiplied bj' I — -=^ I, or (l+TjT-y
For instance, if the height of a simple pendulum is 10 inches and
the weight of the balls equal to the added weight, the height of
the weighted governor will be
A=(n-[)xlO
=2X10
-20
Thus it is evident that if a weight equal to the combined weight
of the balls is added, the height of the governor will be doubled.
If the belt driving the governor slips off or breaks, tha baJia. -wU..
154
STEAM ENGINES
drop, with the result that the engine will "run away." To diminish
this danger many governors are provided with some kind of safety
stop which closes the valve when the governor loses its normal
action. Usually a trip is provided which the governor does not
touch in its normal positions, but which will be released if the halls
drop down helow a certain point.
Spring Type. In many cases a spring is used in place of the
weight. This type of governor b frequently used on throttling
engines, and it consists of a pen-
dulum governor with springs
added to counteract the centrif-
ugal force of the balls. Thus the
height and sensitiveness are in-
creased. Fig. 90 shows the ex-
terior view of a Waters governor
and Fig. 91 shows the same
governor having the safety stop.
In this governor the weights are
always in the same plane, the
variation in height being due to
the action of the bell-crank levers
connecting the balls and spindle.
When the balls move outward,
the spindle mo^■es downward and
I tends to close the valve. The
governor balls are caused to. re-
volve by means of a belt and bevel
gears. The valve and seat are
shown in section in Fig. 92. The valve is a hollow cylinder with
three ports through which steam enters. The seat is made in four
parts, that is, there are four edges that the steam passes as it enters
the valve. The valve, being cylindrical and having steam on both
sides, is balanced, and because of the many openings only a small
travel is necessary.
Shaft Qovemor. Usually some form of pendulum governor
is used for throttling engines. For governing an engine by varying
the point of cut-off, shaft governors are generally used, although the
Corliss and some other engines use pendulum governors for thispur-
ric.92. SwlIonofV
STEAM ENGINES 155
pose. Cut-off goveraors, which are called shaft governors because
they are placed oii the main shaft, are made in many forms, but their
essential features are the same. Two pivoted masses or weights
are arranged symmetrically on opposite sides of the shaft and their
tendency to fly outward when the speed increases is resisted by
springs. When in action the outward motion of the weights causes
the admission valve to close earlier, and the inward motion causes
it to close later. This change is effected by altering the position of
Fie. S3. Diavrsm ShowiDg Action of Buelujra Sbsft Oi
the eccentric, either by changing the eccentricity or the angular
advance.
Shaft governors are made in a gfeat variety of ways, no two
being exactly alike. If the principles of a few types are understood,
it is easy to understand others.
Buckeye Type. The valve of the Buckeye engine is hollow and
of the slide valve type. The cut-off v^ve is inside. The change of
cut-off is due to the alteration of the angular advance, the arrange-
ment of the parts which effect this alteration being shown in Fig. 93.
A wheel which contains and supports the various parts of the gov-
156 STEAM ENGINES
emor h keyed to the shaft. Two arms, having weights ^ ^ at the
ends, are pivoted to the arms of the wheel 6 6. The ends having the
weights are connected to the collar on the loose eccentric C by means
of rods B B.
When the weights move to the portion indicated by the dotted
lines, the eccentric is turned on the shaft about a quarter of a revo-
lution in the direction in which the en^ne runs, that is, the eccentric
is advanced, or the angular advance is increased; tlus makes cutoff
occur earlier, as shown by the table presented in "Valve Gears." If
the en^ne had a angle rIiuu slide valve, the variation of the angular
Diignin ShairiDa Aclion of Btrsichl-IJne Type of Shalt Qove:
advance would produce too great a variation of lead; but as this
engine has a separate valve for cut-off, admission is not altered by
the cut-off valve.
The springs FF balance the centrifugal force of the weights;
the weights ^^ are varied to suit the speed; and the tension on
the springs is altered by means of the screws eo. Auxiliary springs
are added in order to obtain the exactness of regulation necessary
for electric lighting. These springs tend to throw the arms outward,
but act only during the inner half of this movement.
StraighULine Typ?. Fig. 94 shows the governor of the Straight-
line engine. It has but one ball B, which is linked to the spring S
STEAM ENGINES
157
and to the plate DE, on which Is the eccentric C. When the ball
flies outward in the direction indicated by the arrow F, the eccentric
is shifted about the pivot 0, the links moving in the direction of the
arrow H, The ball is heavy and at a considerable distance from
the center, hence it has a great centrifugal force and the spring must
be stiff. The governor of the Buckeye engine alters the cut-off by
changing the angular advance, white the Straight-line engine gov-
ernor changes the travel of the valve. The latter type of valve is
very common.
Inertia Form. The well-known Rites inertia governor. Pig. 95,
is a form of shaft governor largely used for certain types of engines.
This governor regulates the
speed of the engine by shifting
the eccentric, thus changing
the valve travel and increas-
ing or decrea^ng the angular
advance, depending on the
speed conditions. It differs in
its operation from the centrif-
ugal shaft governor previous-
ly considered, in that it makes
use of the inertia of two large
weights instead of centrifugal
force. To understand this
action, it first becomes nec-
essary to know something
about its construction.
The governor consists essentially of a heavy arm A pivoted at
E to the flywheel. This arm carries two heavy weights at B. The
eccentric D is fastened to the arm by three countersunk screws, as
shown, and moves with reference to the engine shaft whenever the
weights B cause the arm A to move about its pivot point. Fas-
tened to the flywheel arm and the governor arm A is the spring C,
which brings the arm A back to its normal position when the engine
is not operating. This spring also has cert^n other functions to
perform in the operation of the governor.
The action of the governor is such that the vsive experiences
very much the same movement as in the centrifugal governor. A&
158 STEAM ENGINES
the engine speeds up, the tendency of the heavy arm A is to lag behind
the flywheel. This lagging action controls the position of the eccen-
tric so that the valve travel is reduced, thus limiting the amount of
steam that enters the cylinders. If, after the engine is operating at
a imiform rate of speed, an increase of load suddenly occurs, the
motion of the engine shaft and fl^nvheel will be slightly retarded and
the engine will commence to **slow down." On account of the energy
stored up in the governor arm and the weights BB, they will not be
so quickly affected, hence the governor will be moving sUghtly faster
than the sfiaft. As a result the eccentric position with reference to
the shaft will be changed, and the valve travel increased, thus per-
mitting more steam to enter the cylinder, increasing the power com-
mensurate with the added load. If for any reason the engine takes
a sudden spurt in speed, the tendency of the governor is to fall back-
ward, so to speak; and if the engine is suddenly slowed down for any
cause, the tendency of the governor is to plunge forward; hence the
valve travel is shortened or lengthened according to which action
takes place. This t^Tpe of governor gives very close regulation when
properly constructed.
ERECTION AND OPERATION OF STEAM ENGINES
The limited scope of this work will not permit of an exhaustive
study of these two important details — ^the erection and operation of
steam engines; only the general principles governing each will be
pointed out.
ERECTION
Foundations. When about to erect an engine the first requisite
is the foundation, the character of which will, of course, depend upon
the type and the size of the engine. It should be built according to
plans submitted by the engine builders, no changes of material con-
sequence being made without the approval of the builders. It
should be neither connected with nor in close proximity to any sup-
porting column or columns of the building, as vibrations of the engine
will be transmitted to the building which might prove to be disas-
trous. The foundation should be built upon a solid bottom, but if
this is not obtainable at the depth required by the foundation plans,
the base of the foundation should be extended in all directions in
STEAM ENGINES 159
order that the bearing surface may he increased. In the case of the
horizontal engines the nearer the center of gravity of the foundation
is placed to the center line of the engine, the more effective will be
the foundation. In sudi cases, therefore, it is preferable to have an
extended bearing surface rather than one of considerable depth. The
foundation bolts and washers should be carefully located in accord-
ance with the furnished plans. A space of one inch or more should
be left around each of the foundation bolts. This may be obtained by
using pieces of short iron pipe or old boiler tubes aroimd the bolts,
care being taken that they do not extend above the foimdation, so
as to prevent the proper tightening of the bolts after the engine is
placed in position. After the engine is properly set, the space left
around the foundation bolts should be filled with the best cement
mortar, so as to insure their permanency. The foimdation should
be a solid one and built of brick, stone, or concrete.
Brick. When brick is used, a hollow square effect may be con-
structed and the open space filled with a mixture of concrete, con-
sisting of one part cement and three parts sand and gravel.
Concrete, When making a concrete foimdation, suitable forms
must first be constructed to receive the concrete. Crushed stone or
clean gravel or both may be used, care being taken to wash the gravel
free of all clay. A good mixture for ordinary foundations is one hav-
ing the proportions: 1: 2J: 5. That is, 1 barrel, or 4 bags, cement,
2J barrels, or 9.5 cubic feet, of sand, and 5 barrels, or 19 cubic feet,
of gravel or stone. If the foundation is to be waterproof, careful
consideration must be given to the proportioning of the mixture. If
the foundation covers considerable area and is not very deep, the
mixture should be richer in cement; if, however, the foundation is
very deep, a poorer mixture may be used at the bottom and a richer
one near the top.
The cement, gravel or stone, and sand should first be thoroughly
mixed in the dry state and the water added while the mixing process
continues until the mass is well mixed and thoroughly wet. After the
mixing is complete, the concrete should be laid in layers from 6 to 9
inches deep and well ranmied until solid. The ramming of the concrete
is an absolute necessity in order that a solid foundation may be secured.
WTien the foundation has been completed in accordance with
the furnished plans, suflBcient time must elapse before any machiae^^i
160 STEAM ENGINES
is placed thereon in order to insure a proper setting of the cement.
When the concrete has set sufficiently, it should be inspected to see
that no omissions or errors have been made, after which the engine
may be unpacked and prepared for setting. If the foimdation is a
large one, an inspector should be on hand at all times to follow the
work and see that no errors are made.
Setting the Engine. Upon the accuracy and thoroughness of
the setting of the engine, in a large measure depends its successful
operation as to smoothness and efficiency of running. In this proc-
ess there are a great many things to be considered. First, the base
and sub-base must be carefully cleaned and set in position. Next,
the crank shaft, cylinders, piston, crosshead valves, and other details
must be carefully placed in position and alignment made according
to the plans of the builders. As all of these details require skill, an
inexperienced person should not attempt the setting up of an engine.
It is always preferable, when possible, to obtain an experienced man
from the engine builders.
Installation of Attachments. In addition to the erection and
setting of the engine proi)er there are various attachments and aux-
iliaries that require care and skill in their proper installation. The
steam and exhaust piping as well as the cylinder drainage should be
carefully attended to. The piping should be of ample size, all bends
should be easy, and gate valves should be used whenever possible.
The piping should have a gradual fall from the boiler to the engine,
at or near which should be placed a separator.
Separator, The separator should be of approved design, and
care must be taken to carefully provide for drainage in order to insure
the removal of the water, otherwise the separator might form a
reservoir for water and thus endanger the engine more with its use
than without. In addition to being a safeguard against water ham-
mer, when properly attached, the separator also improves the steam
economy of the engine, since it removes the most of the entrained
moisture which is carried from the boiler through the steam
pipes.
Exhaust Pipes. The exhaust pipes should be of ample area to
take care of all exhaust steam, and safeguards should be used to insure
no backing up of the condensed exhaust into the cylinders. To this
end, sharp bends should be avoided and gate valves should be used
STEAM ENGINES 161
if valves are necessary, as by their use the area of the pipe is less
reduced than by other forms of valves. Check valves should be
avoided whenever possible.
Cylinder Drains. The cylinder drains should be of sufficient
area to care for all condensed steam in the cylinders and so attached
to the cylinders and the exhaust pipe or receiver that no pockets
will be formed for the accumulation of water. In the case of com*
pound engines the cylinder drains of the high and the low pressure
cylinders should not be connected together, but separately connected
to the exhaust or other main drain. In condensing engines the cyl-
inder drains should always go into the exhaust drain if it is low
enough to admit of proper drainage.
OPBRATION
Let us now turn our attention to the operation and manage*
ment of an engine. It should be borne in mind that many sug-
gestions as to the proper alignment and adjustment of bearings, the
adjustment of valves, and the consideration given lubrication will
be applicable both to the first setting up of the engine and also to the
daily operation afterwards.
Competent Engineer a Requisite. The operation of an engine
should be conmiitted to a careful, skillful, and reliable man. This
is especially true in the case of modern well-equipped plants which
represent quite an outlay of capital. In many of the smaller plants,
however, not much attention is given to the matter and we find, as
a result, men holding positions as operators who know very little
about their business. Under such conditions the plants are seldom
operated efficiently.
As a suggestion of some of the duties of a man in charge of a
modem plant, which also suggest the amoimt of judgment and expe-
rience required, the following general instructions are presented.
Care of Bearing Caps. The caps on the main bearings should
always have sufficient liners underneath to enable the nuts on the
bearing studs to draw the cap down tightly upon them and not pinch
the shaft, which should be free to revolve in its bearings without
unnecessary play.
The caps should be removed occasionally as conditions demand
in order to clean out the oil grooves which are chiy^jedvw^^H^'^isS^^^
162 STEAM ENGINES
metal, as the passages may become clogged with dirt or other for-
eign matter.
Adjustment of Connecting Rod Box. In adjusting the connect-
ing rod box at the crank pin end, the same general rules should be
observed regarding the liners under the cap — ^the large nuts drawn
solidly upon it, the small nuts firmly jammed and the cotter pins
placed in position. The adjustment of the box should then be
tested with a lever about 12 inches in length, the adjustment being
so made that with a lever of this length the operator can easily move
the end of the connecting rod sufficiently to take up the side play
between the flanges on the crank pin and the end of the box. The
adjustment should never be made so close that this side movement
can not be observed. •
The adjustment of the connecting rod box at the crosshead pin
should be made by placing the crank on the center nearest the cyl-
inder; then with a wrench provided for that purpose, slack off both
wedge screws at the upper and lower sides of the connecting rod,
and draw the wedge up until it is solid against the box; then slack
off one screw about a sixth of a turn, and draw up the other so as to
firmly lock the wedge.
Lining Up Crosshead. The crosshead should be lined up between
the guides, while disconnected from the connecting rod. When in
this condition the crosshead should be so lined that it can be easily
pulled from one end of the guides to the other with a short lever.
The crosshead should never be run very close, and should always
be free enough to allow long and continuous runs without heating
the guides to the degree that they would be uncomfortably warm
to the touch.
When making any adjustments of the crosshead, the operator
should assure himself that the lock nut which prevents the piston
rod turning in the boss of the crosshead is securely placed.
Adjusting Eccentric Strap. The eccentric strap adjustment is
made by liners placed between the halves of the strap and double
nutted bolts. When adjustment is necessary, the other end of the
eccentric rod should be disconnected and, after drawing up the strap
bolts, it should be tested by gi\nng the strap a half revolution about
the eccentric. If it is found that the friction between the strap and
the eccentric is sufficient to support the weight of the rod, the bolts
STEAM ENGINES 163
should be loosened and liners replaced until the strap moves freely
without lost motion. The double nuts should then be locked and
the cotter pins replaced in the ends of the bolts.
Qovernor. The governor should be adjusted to meet the differ-
ent conditions of speed and steam pressure and the degree of regula-
tion required. As governors differ so much in design and detail of
construction, it is not possible to give any general rule for their
adjustment. The operator, if desired, can usually obtain instruc-
tions from the engine builder for the particular type of governor
in question.
Valve Setting. As a discussion of the setting of the valves and
their adjustment for wear will be found given in 'Talve Gears,"
no consideration of the subject will be presented here.
Lubrication. The lubrication of a steam engine, and especially
of high speed engines, is a very important consideration with both
the designer and the operator, for it is upon proper lubrication that
they must largely depend for a constant and satisfactory operation.
The designer must, therefore, provide ample and eflBcient faciUties
for lubricating the bearings, cylinders, and valves, whereas the opera-
tor must use discretion in selecting his lubricants and the amount to
use after selection has been made.
Choice of Oils, It might be said that only the best oils should be
used. Cheap oils are usually considered expensive at any cost and
should be avoided as they promote excessive wearing of the parts —
causing noisy operation — and may cause serious cutting of the
cylinders. There are two general classes of liquid lubricants now
in the market, namely, mineral and animal oils. There is also a com-
pounded lubricant which is made up of about 5 to 15 per cent of
animal matter and the balance of mineral oil. This compound makes
a very efficient lubricant for some classes of service, as it withstands
the action of the condensation and adheres to the surface of the cyl-
inders, thus giving better results than larger quantities of mineral oil.
In plants where open heaters are used and where the exhaust
steam is condensed and used for boiler feed water, the compoimded
oils can not be used, on account of the danger of the animal matter
getting into the boilers and causing considerable trouble. In such
cases mineral oil must be used, although it may require considerable
more mineral than compounded oil to acco\si^V\^ ^^ >Nites^^^i^^55fc^-
(
164 STEAM ENGINES
Solid Lubricants. Several solid lubricants are used, such aa
graphite, metalliiie, soapstone, and fiber graphite.
GrapkUe when mixed with certain oils is well adapted for heavy
jN^essures. It is especially good for hea\y pressures and low veloci-
ties. Under conditions which require a large amount of cylinder oil,
a small amount of crystal or flake graphite may be used with good
results. Care must be exercised, however, if the exhaust steam b
used for feed water, as the graphite may get into the boilers and
cause inconvenience and perhaps serious trouble.
Metalline is a soUd compound containing graphite. It is made
in the form of soUd cylinders, which are fitted to the holes drilled
into the surface of the bearing. When a bearing is thus fitted, no
other lubricant is necessary.
Soapgtone in the form of powder and mixed with oil or fat is
sometimes used as a lubricant. Soap mixed with graphite or
soap-stone b often used where wood is in contact with wood or
iron.
A preparation called fiber graphite is used for self-lubricating
bearings. It is made of finely divided graphite mixed with fibers
of wood. It is pressed in molds and afterwards fitted to bearings.
For great pressure at slow speed, graphite, lard, tallow, and
other solid lubricants are suitable. If the pressure is great and the
speed high, castor, sperm, and heav>' mineral oils are used.
For low pressure and high speed, olive, sperm, rape, and refined
petroleum give very satisfactory results.
In ordinary machinery, heavy mineral and vegetable oils and
lard oil are good. The relative value of various lubricants depends
upon the prevailing conditions. Oil that is suitable for one place
might not flow freely enough for another.
The quality of oil is of great importance. In many branches of
industry it is imperative that the machinery run as perfectly as
possible. On this account and because of the high cost of machinery,
only first class oil should be used. The cylinder oil especially should
be high grade, because the valves, piston, and piston rods are the
most delicate parts of the engine.
Qiudities of a Good Lubricant, From the foregoing brief discus-
sion of lubricants it will be evident that they must possess certain
qualities which may be enumerated as follows:
STEAM ENGINES
165
The lubricant must be suflSciently fluid, so that it will not in
itself make the bearing run hard.
It must not be too fluid or it will be squeezed out from between
the bearing surfaces. If this happens, the bearing will immediately
heat and begin to cut. The heating will tighten the bearing and
increase the pressure and the cutting.
It must not gum or dry when exposed to the air.
It must not be easily decomposed by the heat generated. If it
should be decomposed, it might form substances which would be
injurious to the bearings.
It must not take fire easily.
It must contain no acid and should form no acid in decomposing,
as acids corrode the bearings.
Both mineral and animal oils are used as
lubricants. Formerly animal oils were used
entirely, but they were likely to decompose at
high temperatures and form adds. It is impor-
tant in using high pressure steam to have "high
test oils," that is, oils which will not decompose
or volatilize at the temperature of the steam.
It was the difiiculty of getting such oils which
made great trouble when superheated steam was
first used. Mineral oils will stand high tempera-
tures verj' readily, and even if they do decompose,
they form no acids.
Common Oilers. Engines are lubricated by
means of oil cups and wipers placed on the p^ ^^ 8t»nd»rd Typ*
bearings wherever required. They are made in "' ^"p'" **" *^''p
many forms. Formerly, the oil cup was made with a tube extend-
ing through the oil. A piece of lamp wick or worsted leads from
the oil in the cup to the tube. Capillary attraction causes the
oil to flow continuously and drip down the tube. When not in use,
the lamp wick should be withdrawn. This type of oil cup is now
seldom used.
The oil cup shown in Fig. 96 is simple and economical. The
opening of the valve is regulated by an adjustable stop. The oil
may be seen as it flows drop by drop. The cj'Iindrical portion is
made of glass, so that the operator can see how much oU there is in
the cup without opening it
STEAM ENGINES
A form of wiper crank pin oiler is shown in Fig. 97. The oil
cup is attached to a bracket. The oil drops from the cup into the
sheet of wicking or wire cloth
and is removed at each rev-
olution of the crank pin by
means of the cup which is
attached to the end of the
connecting rod. This form of
oiler works very satisfactorily
at slow speeds.
Cetiirifiigal Oiiera. Yig. 98
K«. 97. Form of Wip« Cr«i Pin Oiler "hoWS & CCntrffug^ oilillg de-
vicc which operates verj' sat-
isfactorily at all speeds. The oil flows from the oil cup through
the tube to the small hole in the crank pin by centrifugal force. It
readies the bearing surface by
nieuns of another small hole.
Cylinder Lubrication. In oiling
the valve chest and the cj'linder,
the lubricant must be introduced
agunst the pressure of the steam.
This may be done in several ways,
in each of which it is introduced
into the steam Iwfore it reaches
the valve chest and is carried
by the steam to the surfaces to
be lubricated.
By Oil Pumps. The oil may
be forced into the steam pipe by
a small hand pump or, in large
engines, by an attachment from
the engine itself. Tlie supply of
oil is, of course, intermittent if the
pump is driven by hand, but (continuous and economical if driven
by the engine.
By Sight-Feed Lvbricalors. The most common device for feed-
ing oil to the cylinder is that which introduces tlie oil drop by drop
into the steam when it is in the steam pipe or steam chest. The oil
I. BS. Cenuifuciil Oilir
STEAM ENGINES
167
becomes vaporized and lubricates all the internal surfaces of the
engine.
Fig. 99 shows the section of a sight-feed lubricator, which must
be placed on the steam supply pipe in a vertical position above the
throttle. The reservoir is filled with oil. The pipe B, which
connects with the steam pipe, is partly filled with condensed steam
which flows down the small curved pipe E to the bottom of the chann
her 0. A small portion of
the oil is thus displaced and
flows from the top of the res-
ervoir down the tube F
by the regulating valve D,
and up through the glass
tube S, nhich is filled with
water It enters the mam
steam pipe through the con-
nection A The gauge glass
G indicates the height of
water in the chamber To
fill the lubricator, close the
regulating valve D and the
valve in pipe B; the oil
chamber can thus be drained
through the cock C, and
filled. If the glass S be-
comes clogged, it may be
cleaned by closing valve D
and opening the small valve
//. This will allow the steam to blow through the glass. After
cleaning close valve // and allow glass S to become filled with
water before opening the feed valve. The amount of oil fed to
the cylinder can be regulated by opening the valve D the proper
amount. The exact quantity of oil necessary for the engine is not
easily determined. For ordinary sizes it is from one to four drops
per minute, depending on the conditions.
Instrudums for Proper Lvhrication. In slow speed endues it is
not a difficult matter to attend to the oiling; all the parts are mov-
ing slowly and can be readily examined and oUed. 1!<\».-k3 \a:^«s«*^
Hi. 99. BeoUoD of ^ht-Feed Lubricator
168 STEAM ENGINES
engines run so fast that it is impossible to examine the various parts,
and special means must be provided for lubrication. It is especially
important in high speed engines that there should be no heating.
In order to avoid the danger of neglecting to oil a bearing of a
high speed engine, it is customary to have all the bearings oiled from
one central source. All the oil is supplied to one reservoir, from
which pipes lead to all bearings. If this is not done, large oil cups
are used, as a rule, so that oiling need not be attended to as frequently.
In some high speed engines the moving parts are enclosed and
the crank runs in a bath of oil. This secures certain oiling and is
very effective. All the bearings may be inside this crank case, so
that all are oiled in this way. It is thus impossible for a careless
operator to overlook one point and so endanger the whole engine.
Starting the Engine. Before starting an engine, the oil cups
should be started feeding, grease cups screwed down, and the gov-
ernor and other parts of the valve gear oiled. The cylinder lubri-
cator should be started before the engine so that the oil passages
will contain oil. The cylinder drain cocks should be open so that
any condensed steam in the cylinder will be removed without injury
to the cylinder. These precautions having been observed, the
throttle may be opened slowly and the engine started and gradually
brought to the required speed.
After starting the engine, notice should be taken of the governor
and all the lubricating app£t)*atus to see that each is properly per-
forming its function.
When the engine is to operate condensing, the condenser should
be started first, if it is in such a position that the water in the
exhaust can drain into it. If the condenser is above the engine and
no means are provided for removing the water, the engine should be
started non-condensing. When a jet condenser is used, the quan-
tity of injection water should be increased as the load is increased;
the amount being determined by the conditions of the vacuum and
temperature of the discharge water, which should be from 100** to
110®F. If the water is colder than this, it would denote that more
injected water is being used than is required.
The foregoing suggestions and indicated precautions are only
a few of the more important things that will arise in the course of the
erection, setting, and operation of an engine. The one performing
STEAM ENGINES 169
these various duties must at all times exercise good judgment and
act according to what his past experiences and that of others have
taught under similar circumstances.
ENGINE SPECIFICATIONS
Selecting an Engine. The engineer who has the responsibility
of selecting an engine for a given class of service has no small task
to perform, if he carefully analyzes all the factors entering into the
problem. If the installation contemplated is to be an extensive or
expensive one, expert advice should be solicited. Since this is not
always to be had, a few suggestions will be given as to how best to
proceed when one has to specify an engine for a given service. Con-
sider for the time being that an expert consulting engineer is not avail-
able and a rather inexperienced person, or non-technical man, who
knows little about the theoretical questions that should be given
consideration, has to select the engine. In this case the most satis-
factory procedure to follow would be to go to some reliable engine
builder and ask him to build or specify an engine that would per-
form the service required. Having only one builder intrusted, the
item of expense would not be chief in his consideration since there
would be no competition, therefore the builder would build or specify
the best engine possible for the service. If the funds available
are limited or must be closely conserved, the intended purchaser may
state the limits of cost and then require the builder to come within
those limits. It would also be wise on the part of the purchaser
to require a guarantee as to the performance of the engine and its
maintenance cost for a given period of one year or more.
Drawing Up Specifications. If the purchaser is a competent
engineer or he has in his employ such a person, a complete set of
specifications may be drawn up and submitted to several engine
builders for competitive bids. The specifications submitted should
cover in detail the service for which the engine is to be used, the
speed at which it is to operate, the type of valves and valve gear
desired, the per cent of variation permissible in its governing, and
many other items as to the design and detail of construction. Most
specifications also specify within what limits the engine must operate,
as to the amount of steam used per indicated horsepower per hour,
and the range of mechanical efficiency that mvxsl V«, ^XXalicBR^. K^g^sy-
170 STEAM ENGINES
vision should be made in the contract as to the conditions under
which the acceptance test will be made and by whom.
The form of specification usually submitted by the builders
and which in general will be like those written by an engineer when
requesting bids, is submitted herewith. This may be taken as a
typical specification, the items being changed to meet different con-
ditions of service as the particular case demands.
SPECIFICATIONS OF A VERTICAL CROSS-COMPOUND, SIDE-
CRANK, ENGINE, ARRANGED FOR lOOO-K.W. DIRECT
CONNECTED GENERATOR, 60 CYCLE ALTERNATOR
Size, Power, and Dimensions
Diameter of high pressure cylinder, 27 inches.
Diameter of low pressure cylinder, 54 inches.
Stroke, 42 inches.
Hevolutions per minute, 120.
Initial steam pressure, 125 pounds, 26 inches vacuum, condensing.
Rated load in indicated horsepower, 1,520; cut-off, 26/100.
At ^ cut-off, indicated horsepower, 2,100; maximum cut-off, 7/ 10.
Estimated total weight of engine, 346,000 pounds.
Weight of wheel, 92,000 pounds. Diameter, 16 feet. Face, inches.
Diameter of bearings, 19 inches. Length, 35 inches.
Diameter of shaft between bearings, 22 inches.
Diameter of crank pin, 9 inches. Length, 8 inches.
Diameter of crosshead pin, 8 inches. Length, 8 inches.
Bearing surface of crosshead, 17 inches by 20 inches.
Diameter of piston rod, 5 inches.
Diameter of throttle valve, 12 inches.
Diameter of exhaust opening, 22 inches.
Workmanship and Materials
The workmanship, finish, fitting, and materials will be first-class in every
particular. All forgings will be of open-hearth steel or hammered iron, as
hereafter specified. All castings subject to wear, such as cylinders, guides,
pistons, etc., will be poured from mixtures containing charcoal iron, graded
according to the size of casting in order to secure the proper hardness and
closeness of grain.
The engine will be made to gauge and interchangeable. This feature
will be thoroughly carried out.
Flat surfaces will be scraped to surface plates, and surface and cylindri-
cal grinding will be used where advantageous.
Guarantee
We guarantee the workmanship and materials in the engine to be first-
class and in fulfillment of our guarantee we will give a duplicate to take the
place of any part that may prove defective in material, workmanship, or
design within one year after the engine is started.
STEAM ENGINES 171
We guarantee the engine to regulate from no load to full rated load within
2 per cent variation of' speed.
We guarantee the engine to run in a smooth and proper manner with-
out undue heating or vibration.
Cylinders
The cylinders and steam chests will be neatly covered with sheet iron
lagging, enclosing a thick layer of the best quality of asbestos or magnesia
fiber. The cylinder and steam chest covers will also be provided at each end
with thin iron castings or covers. The cylinders will be provided at each
end with a patent combination relief-valve and drip-cock of large diameter,
adjustable to open automatically at any pressure desired. Being operated
by hand as drip-cocks, these will not stick or become inoperative from dis-
use, but will relieve dangerous pressure from water or other causes.
Jackets and Receiver
The high pressure cylinder will be steam-jacketed and there will be a
receiver of large capacity between cylinders.
The receiver will be filled with seamless brass heating coils containing
steam at boiler pressure. The high pressure jacket and these coils should
be piped in series, so that steam will pass through in the order named, and
since the steam in the low pressure coils is hotter than the receiver steam,
the latter will be considerably superheated upon entering the low pressure
cylinder, and enough of the former will be condensed in the coils to cause
brisk circulation in the high pressure cylinder jacket which is necessary
to its efficiency. It is the aim of this arrangement to keep the steam dry
throughout its course through the engine without the loss of any portion of
heat of the jacket to the exhaust steam. The water condensed in jackets
and in the coils should be returned to the boiler.
Valves
Both cylinders will be four-ported and provided with valves of the flat
gridiron t3rpe of our standard form.
The valves slide crosswise of the cylinder upon gridiron seats, which are
separate and removable from the cylinder itself. Since the valves are of
the gridiron t3rpe, a very small stroke is necessary to give full opening, and
they move with an intermittent motion, standing still when closed, and only
require power to operate when open and relieved of steam pressure. The
clearance is reduced to about one-half of that necessary i^ith valves of the
Corliss type.
These valves possess the follow^ing advantages:
They give rapid opening of port with the least amount of wear and
power reauired to operate.
The clearance space is reduced to a minimum.
They will not stick when the engine is started, and are easy to keep
lubricated.
They wipe over and wear evenly, are unbalanced, and hence loill be
tight when old as well as when new.
Valve Gear
The main valves will be driven by a fixed eccentric controlling the admis-
sion of the steam and the opening and the closing of the exhaust. The cut-
ting off of the steam will be effected by the cut-off valves which are con-
trolled by the governor.
172 STEAM ENGINES
The valve gear is positive, composed of simple levers and links, and the
cut-ofif can take place at any point between zero and the maximum cut-off.
The cut-off, except at light loads, occurs when the main and cut-off valves
are moving in opposite directions, and the cut-off is as sharp as with a releas-
ing type of valve gear notw^ithstanding the short stroke used.
The cut-off is varied simultaneously upon all the cylinders in such a man-
ner that the work done in each is approximately equal, as is also the drop
in temperature of steam in each. This adds to smooth running and gives
best distribution of steam for economy at all cut-offs under variable loads.
The valve gear will be constructed in the most substantial and durable
manner, and in such a way as to equalize the cut-off at both ends of the cylin-
ders for all cut-offs. Rock-shafts, pins, and links will be made of open-
hearth steel. Connecting links will be fitted with bronze ends having quick
taper key adjustment. The eccentric straps will be lined with babbitt
hammered in and bored out. The rock-shaft bearing will be babbitted
and adjustable.
Governors
The governor will be situated on the main shaft of the engine. A change
in position of the centrifugal weights revolves the eccentric controlling the
position and motion of the cut-off valves around the shaft and varies the
point of cut-off.
All the bearing pins in the governor will be made of tool steel hardened
and ground, turning in bearings bushed with phosphor bronze. The cen-
trifugal force of each governor weight is resisted by a plate spring through
a pin having hardened steel points resting in phosphor bronze cups, one at
the end of the spring and the other at the center of gravity of the governor
weight. The centrifugal force of the governor weights is thus opposed in a
direct and frictionless manner without causing pressure or friction on the
pins upon which the governor weights swing. This governor will regulate
the speed of the engine with a closeness and certainty impossible with a
fly-ball governor, and its action is unaffected by wide and sudden fluctua-
tions of load. The governor will control both cut-off eccentrics.
Pistons, Piston Rods, and Stuffing Boxes
The pistons will be cored out and provided with internal ribbing, mak-
ing them very light and strong. They will be secured to the piston rod by
being forced upon a taper, with shoulder beyond, and by a nut, with a simple
but efiicient locking device. The pistons will be provided with cast-iron
packing rings.
The piston rods will be of open-hearth steel running through deep stuff-
ing boxes and babbitted glands. The rods will not touch the heads — which
will be bored large — bronze rings fitting the rods in the bottom of each
stuffing box and preventing escape of packing to the interior of the cylinder.
Low pressure piston will be of steel.
Framing
This will consist, for each cylinder, of a deep and massive base contain-
ing the main bearings. On the back of each base will stand a very heavy
rectangular column, as shown in the blue print, securely bolted to a heavy
frame head. In front the frame heads will be connected to the bases by
forged steel columns l>olted by flanges forged solid with the columns. The
STEAM ENGINES 173
rear column will support the cylinders when the forged columns in front
are removed, facilitating the placing of shaft and other parts.
Guides, Crossheads, and Crosshead Pins
The guides will be separate from the frame and adjustable for wear with
an oil dish at the bottom which, together with a thin brass fringe upon the
bottom of the crosshead, forms an efficient self-oiling device.
The crossheads will be of open-hearth steel fitted with babbitted cast-
iron shoes.
The crosshead pins will be of open-hearth steel flattened on two sides to
prevent wearing oval.
Connectinq Rods and Boxes
The connecting rod will be of forged steel, provided with gib and key
ends. The straps will be provided with pinching bolts which will prevent
spreading. Both crank and crosshead pin boxes will be lined with babbitt
hammered in and bored out.
The body of the connecting rod will be made of larger section than the
piston rod, being designed properly for the added strain due to its length
and angular motion.
Shaft, Crank Pin, and Disk
The shaft will be piled and faggoted hammered iron forging.
The crank disk will be made with counterbalance, of a mixture contain-
ing charcoal iron. The crank pin will be made of forged steel. The shaft
and crank pin will be forced into the disk by hydraulic pressure and the disk
will also be keyed securely to the shaft.
Main Bearings and Removable Shells
The main bearings will be fitted with cylindrical shells, lined with babbitt,
hammered in and bored out. These shells can easily be taken out by remov-
ing the cap and simply jacking up the Shaft sufficiently to take the weight
off the bearings, when they can be revolved around the shaft and taken out
without disturbing any other parts of the engine. The shells are made hol-
low for water circulation. This is not intended to be used ordinarily, but
in case dirt or other unusual conditions should cause the bearing to heat, it
often enables the engine to complete its run without stopping.
The main bearings will be provided with a self-oiling device which will
keep them flooded with oil.
Oil Feed System
The feed will be positive and adjustable and the system will be closed,
so that there will be little waste and deterioration of oil. Rings at the ends
of the bearings will throw off escaping oil into close-fitting shields with suit-
able drain pipes leading to a large settling reservoir beneath. A small pump
driven from the valve gear will deliver the oil to a feed tank at each bear-
ing. This tank will be provided with an adjustable feed outlet pipe leading
to the bearings, and with a gauge-glass and by-pass overflow, and can be
filled by hand and used as an ordinary oil cup if it is desired to cut off the
automatic supply while the engine is running.
Flywheel
The wheel will be cast in halves and will be bolted together at the hub
with reamed bolts carefully fitted in holes drilled from the solid, and the : *.
parts will be planed where they join. Steel arrow heaA \kc^ ^w^Xjfe -^^af^*-, Vv^
174 STEAM ENGINES
at the rim. The wheel will be carefully designed throughout in order to
have a large factor of safety, and both edges and face ot rim will be turned
true.
Platforms
Platforms convenient for handling and operating the engine will be pro-
vided as shown in print. These can be arranged to suit the location of the
engine and will be made stiff to avoid vibration. The hand railings will be
of seamless brass tubing, fitted into brass caps or iron posts. The platform
plates will be diamond figured, planed where they join -together and neatly
. fitted. Stairs will be made of channel iron, with cast-iron diamond threads.
Fixtures
The following fixtures will be provided: throttle valve; indicator motion;
complete outfit of sight-feed cylinder lubricators; glass body oil pumps;
grease cups for valve gear; centrifugal crank pin oilers; reservoirs with sight-
feed outlets; oil pipes and wipers for oiling the main parts of the engine con-
veniently and continuousl}'; relief valves for each end of the cylinders; drip-
cocks; wrenches, foundation bolts; and foundation plans.
Contract. After the engine has been selected and the builders
determined, a written contract should be entered into in order to
make it a legal document. A contract, according to Blackstone, is
an agreement upon suflBcient consideration to do or not to do a par-
ticular thing. In the case of the purchasing of an engine, the builder
agrees to build, erect, and put into operation an engine in accord-
ance with the specifications and drawings submitted, which items
become a legal portion of the contract. The purchaser may also
require that the engine be ready for operation in a given time and
that it must also come up to certain requirements in its performance,
as previously mentioned. In consideration of the foregoing, the
purchaser agrees to pay the builders a specified sum of money, either
•
in one payment or more as determined by them. The wording and
statement of the contract should be carefully prepared, in order to
avoid any possible misinterpretation of any of its provisions.
COST OF ENGINES AND OF THEIR OPERATION
The question of the cost of an engine and of its erection and
operation is indeed a very vital one. This cost can not be classified
in a brief way, since there are so many contributing factors that differ
widely in different localities. For example, no well-defined indica-
tion of the cost of operation can be given, and the cost of labor
and material are fluctuating items of expense; therefore, the cost of
the engine can not be stated definitely, since in a brief interval of
time it may be considerably more or less. Many articles appear
STEAM ENGINES
TABLE III
Prlc« of Slnfle Cylinder Corllu Enrlaes, Set and Erected
81» of
Cylinder. iDcho
?o";^
as
Coal of
^^
SSU'
Tot^CoM
16X36
125
11950
S32S
S210
SISO
«2665
1SX36
155
2150
376
240
200
2965
18X48
200
2500
425
260
220
3605
20X48
230
2850
625
275
250
3900
22X42
250
3000
560
300
310
4160
24X48
320
4000
700
375
390
6465
28X48
425
ai50
900
600
800
7650
30X48
490
5800
1200
600
1070
8670
from time to time in the leading engineering papers which give val-
uable information upon such matters and usually this infonnstioQ
is correct since it is given currently with the ascertained cost of
various items. It is, therefore, suggested that if the latest and per-
haps most authentic information is desired upon these items of
expense that such articles as appear in the papers mentioned should
be consulted.
Engine Costs. As an indication of what such expense will be
Tables III and IV, aa devised by Dean C. H. Benjamin, are pven.
TABLE IV
Cost of High Speed, Single Cylinder Engines
1
N
E .
P
^
J,
is
I'
a
III
^1
^1
1
.50
9X10
100
300
S695
$46
«66
.70
»10
$S85
75
10X12
100
300
890
50
76
70
15
IIOO
100
12X12
100
290
1085
.W
80
70
15
1300
125
13X14
100
275
1260
70
05
70
17
1512
150
15X14
14X16
100
245
1595
80
110
75
20
1880
200
18X16
100
225
2010
90
140
85
25
23.W
250
19X18
100
200
2800
250
200
100
35
3385
Relative Cost of Operation Items. The cost of the operation
of a steam plant is properly made up of several items, vvt, ^«e*. *st
176
STEAM ENGINES
TABLE V
Cost of lastallatlon and Operation for One Year
Kind of EAgine
Total Cost
Engines and
Boilers
Annual Cost
of Both Engine
and Boilers,
Depreciation
and Interest
Total Tons
Coal Per Year
of 3000 Hours
c
a
•S
t
Labor,
Engine and
Boilers
Cost of Power,
Coal at 92 Per
Ton. 1 Year
Simple Slide Valve Non-con-1
densing J
$29.75
$4.03
6750
$1.02
$5.00
$23.55
Compound Slide Valve Non-1
condenfling f
Compound Slide Valve Condens-l
inff
31.50
29.80
4.38
4.26
5660
4050
1.25
1.25
4.50
3.80
21.45
17.41
Simple CorliRR Non-condensing
Compound CorliH8 Condensing
Triple Corliss Condensing
32.25
30.87
34.25
3.84
3.76
4.28
6075
3375
3110
1.00
1.25
1.50
4.70
3.50
4.00
21.00
16.25
16.00
interest on real estate; interest on investment; maintenance, etc.,
of equipment; fuel; water; supplies; and attendance.
The relative value of these various items for a large central sta-
tion lighting plant was given in the Engineering Mdgazine, May,
1905. Taking the total cost of maintaining the station as 100 per
cent, the following were the average costs of the various items:
Fuel 52.5%; wages 26.4%; water 2.2%; oil and waste 1.8%; rent
4.35%; station repairs 2.2%; steam repairs 5.45%; electric repairs
5.1%.
Annual Operation Expenses. Professor Carpenter in the
Economist summarizes the cost of installation and the operation of
an entire plant for one year of 3,000 hours as given in Table V.
A coal consumption of 4.5 pounds per boiler horsepower per hour is
assumed and the cost given per engine horsepower is for a 1,000 horse-
power engine.
An illustration involving the items given in Table V will serve
to make it clearer. The case of a simple slide valve non-condensing
plant will be considered.
Cost of engines and boilers at $29.75 per horsepower « $29,750.
Annual cost of depreciation and interest at $4.03 per h.p. <= $4,030.
Annual cost of coal at $2.00 per ton =6750X2 =$13,500.
Annual cost of lubricants at $1.02 per horsepower =$1.02X100 =$1,020.
Annual cost of labor at $5.00 per horsepower =$5.00X1000 = $5,000.
ual cost for the last four items =$23,550 or $23.55 per h.p.
STEAM ENGINES 177
The foregoing tables will serve to give some idea of the cost of
engines, also of the cost of operation of a steam plant, but it must be
remembered that the figures given will not be exact for all localities
or for all times, due to the changing influences previously mentioned.
ENGINE TESTS
Importance of Tests. It was mentioned in connection with the
discussion of specifications and contracts that often a guarantee is
given by the builder as to the economical performance of a steam
engine, hence it is required that the engine be tested in order to ascer-
tain whether or not it meets the provisions of the guarantee. While
this is one reason that may be assigned for testing an engine, yet
there are several others of importance. The user from time to time
may want to ascertain the condition of the engine as a whole and
also the condition of particular features such as the valves, etc. For
purely theoretical reasons an engine is often tested in order that
an anal>i:ical study may be made of its performance under various
conditions and in comj arison with other engines of different classes.
Many such tests have resulted in obtaining data, the facts of which
have demonstrated to both the builder and the user possible econo-
mies. Because of the information thus obtained, the builder has
been enabled to design a better engine, and the user to operate his
engine more advantageously. The remarks given will suflBce to
indicate that the ultimate object of an engine test is the determina-
tion of the economy with which the engine produces a given amount
of power. In steam engines the economy, as usually ascertained,
relates to the weight of steam consumed, to the quantity of coal
required to make the steam, or to the number of heat units supplied.
The elementary quantities concerned are accordingly two in num-
ber, viz, the amount of steam, fuel, or heat (as the case may be)
consumed, and the amount of power developed. How to determine
these quantities is the problem.
A. S. M. E. Gxie. The American Society of Mechanical
Engineers (A.S.M.E.) deemed the testing of engines according to
some definite and standard method of such importance that a com-
mittee was appointed to devise a standard code. This, after much
labor and diligent study, was presented to the Society and ^^58^\s^*^
The full report appears in Volume 24 (>^S>4^ , y^^s^ ^^^^ ^ ^^'^itsMcar"
178 STEAM ENGINES
actions. This code indicates the method of obtaining the required
data and also gives a recommended form of report. In so far as the
conditions will permit, this code should be followed. The several
items of the code are sunmiarized as follows:
Methoi> of Conducting Steam Engine Tests — Code op 1902
(/) Object of Test. Ascertain at the outset the specific object
of the test, whether it is to determine the fulfillment of a contract
guarantee, to ascertain the highest economy obtainable, to ascertain
the performance under special conditions, to determine the effect of
changes in the conditions, or to find the performance of the entire
boiler and engine plant, and prepare for the test accordingly.
No specific rules can be given for the preparations for the test
as conditions surrounding each test will require a more or less differ-
ent solution, which must be solved by the one in charge. The one
particular thing to be emphasized at all times is, that in order to
obtain data that is absolutely reliable for the purpose in view, the
one in charge must be vigilant, conscientious, and, above all,
honest.
(^) General Condition of the Plant, Examine the engine and
the entire plant concerned in the test; note its general condition and
any points of design, construction, or operation which bear on the
objects in \Tiew. Make a special examination of the valve and pis-
tons for leakage by applying the working pressure with the engine
at rest and observe the quantity of steam, if any, blowing through
per hour.
If the test is for the purpose of ascertaining the highest efficiency,
the valves and pistons must be made steam- and water-tight.
To test the valves and piston block the fl^-wheel so the piston
will be near one end of the stroke, and turn on the steam. The leak-
age will escape to the exhaust port and will be observable. Another
approximate method is to block the engine as before and having an
indicator on the cylinder, observe the drop in pressure after an inter-
val of time. In a tight engine the fall of pressure will be slow,
whereas in a leaky one it will be fast. Other methods of determining
the amount of leakage may suggest themselves to the engineer in
charge of the test.
(S) Dimensions, etc. Measure or check the dimensions of the
c>'linders in every case, this being done when they are hot. If they
are much worn, the average diameter should be determined. Meash
ure also the clearance, which should be done, if possible, as described
STEAM ENGINES 179
in "Valve Gears.'* If the clearance can not be determined directly,
it can be done approximately from the working drawings of the
cylinder.
14) Coal. When the trial involves the complete plant, embrac-
ing boilers as well as engine, determine the character of the coal to
be used. The class, name of the mine, size, moisture, and quality
of the coal should be stated in the report.
(J) Calibration. All instruments and apparatus should be
calibrated and their reliability and accuracy verified by comparison
with recognized standards. Such apparatus which is liable to
change or become broken during the test, as gauges, indicator springs,
and thermometers, should be calibrated before and after the test.
The accuracy of scales should be verified by standard weights. Any
water meters used should be carefully calibrated before and after,
and during the test if possible. All of the apparatus may be very
easily tested, directions for which may be found in various hand-
books of engineering and often in instruction pamphlets published
by the manufacturers. The method of testing indicator springs is
given in "Steam Engine Indicators."
(6) Precaviion. Make sure that there is no leakage at any of
the connections with the apparatus provided for measuring and sup-
plying the feed water and the steam that could affect the results.
(7) Duration of Teat. The duration of a test should depend
largely upon its character and the objects in view. The standard
test of an engine and, likewise, a test for the simple determination
of the feed water consumption should be continued for at least five
hours, unless the class of service prevents a continuous run of so long
duration.
When the water discharged from the surface condenser is meas-
ured for successive short intervals of time, and the rate is found to be
uniform, the test may be of much shorter duration than when the
feed water is measured to the boiler. The longer the test with a
given set of conditions, the more accurate the work.
The commercial test of a complete plant, embracing boilers as
well as engines, should continue at least one full day of twenty-four
hours, whether the engine is in motion the entire time or not. A con-
tinuous coal test of a boiler and engine should be at least of ten
hours duration, or the nearest multiple of the interval between
times of cleaning fires.
{8) Starting and Stopping a Test. Before beginning to take
readings the engine should be operated a suffi!d«tt^.\«w^gic^<^''^«^
180 STEAM ENGINES
it to become thoroughly heated in all of its parts, and in the mean-
time all of the measuring apparatus should be properiy adjusted.
Having made the preliminary arrangements mentioned, at a given
signal the height of water in the gauge glasses of boilers is observed,
the depth of water in the reservoir from which the feed water is
supplied is noted, the exact time of day is observed, and the test is
held to commence. Thereafter the measurements determined upon
for the test are begun and carried forward until its close. It is con-
venient to begin the test at some even hour or minute, but the impor-
tant thing is to begin the test when accurate readings can be obtained
irrespective of the time. When the time for closing the test arrives,
the water in the glasses should be brought to the same height as it
was at the beginning; if this is not possible, corrections must be made
in the report.
(9) Measurements of Heat Units Consumed by the Engine. The
measurement of the heat consumed requires the measurement of all
the water supplied to the boiler, by whatever means; the tempera-
ture of the water supplied from each source; together with the pres-
sure and quality of the steam, which are to be taken at some point
near the throttle valve. The quantity or steam used by the steam
calorimeter must also be accounted for.
The heat to be determined is that used by the entire engine
equipment, embracing the cylinders and all auxiliary cylinders and
mechanisms concerned in the operation of the engine, including air
pumps, feed pumps, reheaters, etc.
(10) Measurement of Feed Water, or Steam Consumption of
Engine, etc. The method of determining the steam consumption
applicable to all plants is to measure all the feed water supplied to
the boilers and deduct therefrom the water discharged by separa-
tors and drips, as also the water and steam which escapes on account
of leakage of the boiler and its pipe connections and leakage of the
main and branches connecting the boiler and engine. In plants
where the engine exhausts into a surface condenser the steam con-
sumption can be measured by determining the quantity of water
discharged by the air pump, corrected for any leakage of the con-
denser and adding this to the steam used by jackets, reheaters, and
auxiliaries as determined independently.
In measuring the water it is best to carry it through a tank or
tanks resting upon platform weighing scales suitably arranged for
the purpose, the water being afterwards emptied into a reservoir
beneath, from which the pump is supplied.
STEAM ENGINES 181
(11) Measurement of Steam Used by Auxiliaries. Although the
steam used by the auxiliaries was measured as mentioned in item {10) y
yet it is very desirable to ascertain the steam consumption of each
auxiliary independently, in order that a close analysis of the engine
performance can be made. Several means may be employed for
determining the steam consumption of the various auxiliaries, and
since they will be apparent to the operator no discussion of them
will be given, but they are only mentioned in order to emphasize the
desirability of obtaining such data.
{12) Coal Measurement, In commercial tests of the combined
engine and boiler equipment, or those made under ordinary condi-
tions of commercial service, the test should extend over the entire
period of the day, that is, twenty-four hours, or a number of days
of that duration. Consequently, the coal consumption should be
determined for the entire time. If the engine runs but a part of the
time and during the remaining portions the fire is banked, the meas-
urement of coal should include that used for banking. It is well,
however, in such cases to determine separately the amount consumed
during the time the engine is in operation and that consumed dur-
ing the period while the fires are banked, so as to have complete
data for purposes of analysis and comparison, using suitable precau-
tions to obtain reliable measurements. The measurement of coal
begins with the first firing, after cleaning the furnaces and burning
down at the beginning of the test, and ends with the last firing, at the
expiration of the allotted time.
In connection with coal measurements, whatever the class of
tests, it is important to ascertain the percentage of moisture in the
coal, the weight of ashes and refuse, and, where possible, the approxi-
mate and ultimate analysis of the coal. (For discussion of this item
of coal the student is referred to Vol. 22, P. 34, of the A. S. M. E.
Transactions.)
(13) Indicated Horsepower, The indicated horsepower should
be determined from the average mean effective pressure of diagrams
taken at intervals of twenty minutes, and at more frequent intervals
if the nature of the test makes this necessary for each end of each
cylinder.
The indicator diagrams should be taken at regular intervals
but not necessarily simultaneously at the two ends of the cyUnder.
I( the diagrams vary so much as not to give fair results, the diagrams
should be taken more frequently.
The method of attaching, operatiiv^, axvA «Ayx^\1\^%'^^*>^»^^:»^»^
182 STEAM ENGINES
and also the method to follow in obtaining the mean effective pres-
sure are described in "Steam Engine Indicators."
(14) and (15) Testing Indicator Springs and Brake Horsepower.
These items are fully discussed and explained in "Steam Engine
Indicators."
(16) Quality of Steam. When ordinary saturated steam is used,
its quality should be obtained by the use of a throttling calorimeter
attached to the main steam pipe near the throttle valve. When the
steam is superheated, the amount of superheating should be found
by the use of a thermometer placed in a mercury well inserted in the
pipe.
(17) Speed, There are several means for obtaining the num-
ber of revolutions the engine makes per minute. They may be
counted during one minute or some other division of time, a tach-
ometer may be used, but the most reliable results are obtained by
using a revolution counter, such as was illustrated and described in
"Steam Engine Indicators." In using the counter, the total reading
should be taken each time the general test data is recorded. These
revolutions per minute corresponding to the difference in reading of
the instrument can then be computed, knowing the time interval.
(18) Recording Data. Take note of every event connected with
the progress of the trial, whether it seems at the time to l)e impor-
tant or unimportant. Record the time of every event, and time of
taking every weight, and every observation. Observe the pressures,
temperatures, water heights, speeds, etc., every twenty or thirty
minutes when the conditions are practically uniform, and at much
more frequent intervals if the conditions vary. Observations which
concern the feed water measurements should be made with special
care at the expiration of each hour of the trial, so as to divide the
tests into hourly periods and show the uniformity of the conditions
and tests as the test goes forward. W'here the water discharged
from the surface condenser is weighed, it may be advisable to divide
the test by these means into periods of less than one hour.
The data and observations of the test should be kept on properly
prepared blanks or in notebooks containing columns suitably arranged
for a clear record.
(19) Uniformity of Conditions. In a test having for an object
the determination of the maximum economy obtainable from an
engine, or where it is desired to ascertain with special accuracy the
effect of predetermined conditions of operation, it is important that
all tht conditions under which the engine is operated should be main-
STEAM ENGINES 183
tained uniformly constant. This requirement applies especially to
the pressure, the speed, the load, the rate of feeding, the various sup-
plies of water, the height of the water in the gauge glasses, and the
depth of the water in the feed water reservoir.
{20) Analysis of Indicator Diagrams, (a) Steam accounted for
by the indicator. The method of accounting for the steam by use
of the indicator is thoroughly treated in "Steam Engine Indicators,"
so no further discussion will be given here, (b) Sample indicator
diagrams. In order that the report of a test may afford complete
information regarding the conditions of the test, sample indicator
diagrams should be selected from those taken and copies appended
to the tables of results.
The points at which the different events occur should be clearly
marked on the cards submitted with the report.
{21) Standards of Economy and Efficiency. The hourly consump-
tion of heat determined by employing the actual temperature of the
feed water to the boiler, as pointed out in item (P), divided by the
indicated and brake horsepower, that is, the number of heat units
consumed per indicated or brake horsepower per hour — these are the
standards of engine efficiency recommended.
It is useful in this connection to express the efficiency in its more
scientific form, or what is called the "thermal efficiency ratio." The
thermal efficiency ratio is the proportion which the heat equivalent
of the power developed bears to the total amount of heat actually
consumed, as determined by test. The heat converted into work
represented by one horsepower is 1,980,000 foot pounds per hour,
and this divided by 778 equals 2,545 British Thermal Units. Con-
sequently the thermal efficiency ratio is expressed by the fraction
2545
British Thermal Units per hour
{22, 23, 24, and 25) . These sections of the Code deal with purely
scientific investigations, hence they do not essentially enter into com-
mercial tests and will not be given.
{26) Report of Test. The data and results of the test should be
reported in the manner and in the order outlined in the following
report. It is the intention that the report be full enough to apply
to any type of engine, but when not so, or where special data and
results are determined, additional results may be inserted under the
appropriate headings.
Actual Engine Test. To illustrate the application <^1 xc^axcj ^
the items given as obtained f rem lYie Code, ^ulx^J^^xv^^^^^"^"^^^^^
184
STEAM ENGINES
taken and reported upon. This report will serve to give the order
and manner in which data should be tabulated and also the method
in which the report should be worked up.
DETERMINATION OP EFFICIENCY OF A BUCKEYE ENOINB
UNDER DIFFERENT LOADS
The purpose of this seriea of tests on the Buckeye engine located in the
Engineering Laboratory of Purdue University was to determine the beat
efficiency under six different loads, ranging from zero to 1| load, by i load
eteps, the engine running non-condensing and uaing 160 pounds of steam pres-
sure, absolute.
Plan
The Ecro load was determined with the friction brake /, Fig. 100, removed .
and the engine running free. The full load was determined by the brake load
Fig. 100. Buokeye BuiDg Fittsd
Braks uid liuJUe&tora
which the engine carried with 25 per cent cut-off, this being the builders* rating
for this type of engine. The \, }, J, 1, and 11 loads were taken as 25%, 50%,
75%, 100%, and 125%, respectively, of the full load.
Steam pressure was maintained constant at the pressure indicated for
the test. Each test was of one hour duration, the engine having been run
under conditions of the test a length of time sufficient to permit the condi-
tions to become constant.
STEAM ENGINES 185
Method of Conducting Test
Constant steam pressure was obtained by throttling the 5-inch steam
line leading to the engine by means of the pipe line valve. This throttling
action was not sufficient to cause the steam to become superheated.
The revolutions per minute were obtained by means of a revolution
counter.
Indicator diagrams were taken every five minutes, 13 sets of diagrams
bemg obtained for each hour's run.
Barometer readings were taken every 15 minutes.
The amount of water was determined by condensing the exhaust steam
at atmospheric pressure.
Prellmlaary Work
Before commencing the work the engine was placed in as good .condition
as was possible. The governor was adjusted in order to reduce friction; play
was taken up in the valve gear and the valves were carefully set to give equal
cut-off on both ends at full load; all stuffing boxes were repacked; the brake
wheel was turned up and brake recalibrated.
M<. The pressure in the engine supply line was obtained by tapping a }-inch
pipe into the main, about 3 feet from the valve. This }-inch pipe was con-
nected to a large steam gauge which faced the operator of the throttling valve,
thus enabling him to watch the gauge all the time and maintain a constant
pressure.
Observed Data
In each test the following observations were taken:
Steam pressure, constant throughout
Brake load
Revolutions per minute
Weight of condensed steam
Barometer
Indicator diagrams
Results
' Having the above data it becomes possible to calculate the following:
(1) Per cent of cut-off, head end and crank end.
(2) Mean effective pressure (m.e.p.), head end and crank end.
(3) Indicated horsepower, head end and crank end and total.
(4) Brake horsepower (b.h.p.).
(5) Friction horsepower (f.h.p.).
(6) Mechanical efficiency.
(7) Pounds steam, per indicated horsepower per hour and per brake horse-
power per hour.
(8) British Thermal Units per hour, per indicated horsepower and brake horse-
power per hour.
(9) Thermal efficiency.
Constants and Formvlas, The constants of the engine and formulas
employed in obtaining the calculated items in the sunmiarY ^1 tmn^^j^^
follows:
STEAM ENOINES
5-
1
^
k
f
t
^
H
fl
-*■■
I
i
«
^
iy
«
^
^=—
— -
;:?
*<y
"^
.pW^
"V
s
?
ij.„5
^
?
^
1
-1
-'§
-ffS
s
g
rx"'
^
?5
^k
\
qK
N
•s
S
?
1
X
>
J
-§^-
i
^
^,
^
V
.*
s
•l
^
^
*
^-
.
^>
12
8
;
^
5
^
ft
-^
s
s
i
s
1 r 1
STEAM ENGINES
187
Diameter of cylinder, 7.7S inches.
PistoD rod diameter, 1.437 inches.
H.£. area, 47.173 square inches; c.e. area, 45.55 square inches,
lUdiuB of brake arm, 38.25 inches, equals 3. 185 feet.
Clearance, head end 6.15%; crank end, 6.765%.
Normal speed, 220 revolutions per minute.
Heat value of 1 horsepower, 42.42 British Tbermal Units.
Heat value of 1 pound of steam, above 32°F. for 160 pounds absolute
1,192.8 British Thermal tJnita.
Gauge pressure 15 pounds (appronmate) less than absolute pressure.
The horsepower constants are as follows:
H.E.-i.h.p. ConBtant ^.001787. (See "Steam Engine Indicaton.")
C.E. -i.h.p. Constant - .001726.
D.H.P. Constant - .00060695.
Item (3). At observed revolutions per minute (r.p.m.):
H.E.-i.h.p. -.001787Xh.e. m.e.p.Xr.p.m.
C.E.-i.h.p. = .001726Xe.e, m.e.p.Xr.p.m.
Total i.h.p. =h.e. i.h.p. +c.e. i.h.p.
It oft«n happens that the engine is not
operated at the desired speed just at the in-
stant of taking the reading, hence a correction
must be made if the indicated horsepower is to
be expressed and recorded for the normal
speed. Therefore i.h.p. - total i.h.p. X 220 +
observed r.p.m.
Item (4). Atobaervedr.p.m.determined
as follows;
B.H.P.-.OOOeoeoSXpounds brake load
Xr.p.m.
B.H.P, =.0001904 pounds brake load at
1 foot radius Xr.p.m.
At 220 r.p.m., corrected b.h.p. — b.h.p.
X220+ob8erved r.p.m.
Item (5). At 220 r.p.m., the f.h.p.-total i.h.p-b.h.p.
Item (6). At 220 r.p.m., the mechanical elHciency -b.h.p. -t-total i.h.p.
The pounds of steam per hour at 220 r.p.m. — pounds of steam per hour
at observed r.p.m.X220-i-observed r.p.m. The B.T.U. supplied per hour-
corrected pounds of steam per hourXtotal British Thermal Units in 1 pound
steam, at ^iven absolute pressure above 32°F.
Item (7). The pounds steam per i.h.p. per hour = corrected pounds
steam per hour divided by corrected i.h.p.
The pounds of steam per b.h.p. per hour = corrected pounds steam per
hour divided by corrected b.h.p.
Item (8). The British Thermal Units per i.h.p per hour>total British
Thermal Units supplied divided by 160Xcorrected i.h.p.
The British Thermal Units per b.h.p., per hour=total British Thermal
Units supplied divided by corrected b.h.p. X 160.
Item (9). The Thermal Efficiency = 42.42 British Thwctosl. "Vi-ti**
divided by British Thermal Units per i.^i.^. v^ Vova
t^
*f
^rr
i..
•V
sH
_
_
-
-
'
..
^*
-'* 1 1
STEAM ENGINES
TABLE VI
iBdlcator Olagrani Data for Buckeye Enelae Test
Steam Pressure
\60 '^A&s.
CYL.
CARP
NO.
NO LOAD
I^ LOAD
^ LOAD 1
%ao.
HE.P.
%ao.
f^.E.P.
%C.O.
HE.P.
r
r
V
1
.OOO
J. 58
14.73
5.00.
28.41
s
.785
!.32
/3.98
S.52
28. J 7
5
.773
J.05
/4./4
4.98
28.37
4
.?59
/.05
/4.73
4.7/
26.70
5
1.0/}
1.05
f3.6S
£.00
26.82
6
.OOO
LOS
/4.45
4.46
26.78
7
.000
.79
/4./3
4.47
26.30
a
.521
.73
/3.4/
4.7/
26./ 8
9
.675
/.OS
/2.S0
4.7/
27.22
/o
/.B95
/.OS
/2.63
4.97
27.22
//
.675
/.OS
/Z.90
4.7/
27.22
/2
.529
/.06
/4.80
4.73
26.30
/3
.779
/.OS
/Z.44
4.97
27.22
AK
^638
/.073
/3757
4.841
27./ 4
^
/
4.325
-77
/8.SB
7.41
36.59
e
4.325
.76
/850
7.66
36.80
-5
3.80S
.77
/8.67
7.65
36.46
«t
3.360
.77
18.58
7.65
36.20
S
4.055
.77
/S./3
7.65
36.20
6
3.567
.77
/B.$e
7.66
36.30
7
4.340
.77
/8.43
7.65
36.20
a
3.805
.77
/8.37
7.4 1
36.30
s
3.805
.76
/7.70
7.64
3763
10
3.785
.76
/7.95
7.41
378/
//
3.805
.76
17.95
7.65
36.7 S
/:?
3.560
.76
/7.75
740
36.20
13
4.555
-76
/7.9S
7.69
37./ e
AK
3.3445
.7663
/BJ38
7.578
36.655
STEAM ENGINES
TABLB VII
Indicator Uagram Data for Bnckeye Engine Test
Steam Pressure :60*Abs.
CYl.
END
CARD
NO.
^4 LOAD
FULL LOAD
/k/ LOAD 1
%C.O.
HE.P.
%C.O.
M.E.P.
%>C.O.
ME.P.
%
r
1
J 3.6 5
46.70
24.90
63.25
33.92
7 7.60
?
/3.e5
44.95
24.05
63./ 5
3 5.22
rr.eo
J
/3.69
4 4.75
24.35
62.85
35.32
7 7.80
tf
13.88
4 4.75
25.15
63.35
34.90
7-7.00
5
M.40
44.50
24.52
64.65
35.4/
-'6.60
6
/4.S/
45.50
25./ 5
6 4./ 5
35.26
7 7./0
7
/3.85
44.65
24.2/
64.20
34.27
77.55
8
/3.57
4 5. J 5
25.05
63.76
34.87
7 7.05
9
/3.65
44.90
25-/5
64.90
36.2/
78.95
/O
/4.J5
46.20
24.35
63.35
34.05
77.50
//
/4.70
43.40
24.42
63.2 5
34.07
77.95
/?
J 3.92
44.40
25./ 5
64. /5
34.80
78.03
/3
14. tf
44. /5
25.20
64.50
34.72
77.95
AV,
/3.S8
45.073
24.78
63.80
34.04
^7.537
1
/
/4.05
5 3./ 5
24.80
67.85
3/.a7
a?.05
B
14.50
52.80
24.75
6 7.30
34.25
82.30
J
/4.05
52./S
25./0
68.70
33.5 9
a /.BO
-4
/4.3£
53.45
24.05
67.50
32.59
80.80
S
/4.54
5/. 80
24.67
67.50
33 32
8/. 3/
6
/4.//
53.10
24.80
68.35
32.83
8/.30
r
/4.22
52.55
24.2B
68.4 Q
3283
80.80
8
/4.5 4
52.25
24.6/
68.00
32.83
8/.00
9
/4.28
5/. 80
24.80
68.80
34.25
8/. 80
/O
/4.5 a
5/. 8 5
24.38
69.06
32.90
80.25
N
/4.54
52.25
24.6 O
68.65
33.07
80.75
!2
/4.54
53.30
24.58
68.55
33.52
80.00
/ 3
/4.r6
5 2. J 5
24.90
68.50
32.63
30.20
A-y.
/^.3B
52.527'
24.59
68.30
33.//
e/./o
190
STEAM ENGINES
TABLE Vlll
Performance of
Under Different Cut-offIs
Summary
OBSERVED
1^^
AV, M.E.P.
I.H.P.
I
g
^st:/
29.82
4343
.564
3.945
.289
/SS3
2242
f.^C
227.5
2255
29.83
550.P
.97
/J.76
/&39
5.45
7./ 3
/2,86
/2.JS
53 /.O
222.9
298/
8490 6.2/
27/4
36.66
10.82
/4J0
2432
24^8
8/5.0
2 2 A 9
29.80
/O96,0 /42
45.07
52.53
/7.86
20./0
37.96
37.62
//26.0
2/7.4
29.78
/4O/.0 24j6
63.80
67.74
24.80
25.62
50.42
5/. 00
/*
/3630
209J^
2979
/6/43 34.0
77.54
8/./0
29.00
29.30
38J0
6/,20
C£
HE.
HE.
H£
HC
CE HE
Fig. 74. Ixulioator Diagrams Taken Puring Test of Buokesre Engine
STEAM ENGINES
TABLE VIII— Continued
THE Buckeye Ehqine
Steam Pressures 160* Abs,
OF Results.
B.H-P.
CALCULATED
m
sg^
Pi
=§;
J. 07 37.5
5S25 SOS
S445
5707
PloUed RetvlU. On curve sheet shown aa Fig. 101, are plotted to pounds
brake load at I' radius, the i.h.p., b.h.p., f.h.p., and mechanical efficiency.
On curve sheet shown as Fig. 102, are plotted to horsepower the pounds
steam per i.h.p. per hour, the pounds steam per b.h.p. per hour, the British
Thermal Unit per i.h.p. per minute, the British Thermal Unit per b.h.p. per
minute, and the thermal efficiency.
On curve she^^t shown as Fig. 103, ia plotted a curve which shows the
steam consumption for the different per cents of cutoff.
Conclusions and Comparisons
An examination of the curves shows a marked increase in economy of
the ) load over the 1 load; a smaller increase in economy of the j load over
the i load; and a still smaller increase in economy of the full load over the
I load; but the full load and 1} load have the same steam conaumptioQ per
i.h.p. per hour indicating that the engine is operating roost ecoDomically
throughout this range.
The teats indicate a very good range of economical operation from
J load to 1] load, and although Che steam consumption is higher than the
beat recorded results for other engines of greater horsepower, yet the results
obtained arc very good considering the relatively small site of the engine.
Appendix
The engine under teat was a 71'X15' type "B" Buckegre engine which
had been rebuilt from the old type of flat valve to a piston valve engine. The
following information was supplied by the Buckeye Engine Company:
Lap n', Lead A', Compression 2)', Exhaust laps, i and A', Clearance
fi.6%, Cut-off 25%. Weight of reciprocating parts 150 pounds.
The arrangement of the brake apparatus may be seen in Fig. 100, in which
A is brake lever, B is calibrated brake load arc, C is brake pendulum^»iA.\l
is brake wheel.
192 STEAM ENGINES
Cooling water for the brake enters through a hose not shown in the illiis-
tration. The direction of rotation of the brake wheel is indicated by the
arrow near D. By means of the hand wheel Ef the brake load is applied and
regulated. The brake was carefully calibrated before beginning the test.
Calibration of Constants
jjT? '. A' A * 47.173X15 ^^
H.E. piston displacement » — ■- = .41 cu. ft.
144X12
45.55 X 15
C.E. piston displacement = — '■ = .396 cu. ft.
144X12
TTx. , 0252 ^^^^
H.E. clearance = —-—=6.15%
.41
^ -^ . .0268 « _^ « ^
C.E. clearance =--— =6.765%
.Oi/O
^^ r^ ^ . X 15X47.173 ^,^«^
H.E. - i.h.p. Constant = ,^ ^^^^ - .001787
^ 12 X33000
15X45.55
C.E. - i.h.p. Constant = -- — — —- = .001726
^ 12 X 33000
B.H.P. Constant = .00060695
33000
Thermal Efl5ciency Constant = ———=42.42
778
Tables VI and VII contain information from the indicator diagrams,
and Table VIII is a general summary of the observed and calculated results of
the tests.
Fig. 104 shows sample indicator diagrams taken during the test.
INDEX
INDEX
PAGE
A
American locomobile 45
B
Buckeye engine determination of efficiency of under different loads 184
appendix 191
conclusions and comparisons 191
method of conducting test 185
observed data 185
plan 184
preliminary work 185
purpose 184
results 185
Buckeye steam engine 36
C
Cameron belt-driven pump 68
Compound pumping engine 7
Condensers 123
amount of cooling water per pound of steam 137
cooling surface in surface condensers 138
cost of cooling water determines condenser economy 134
effect of condensation 123
effect of condenser on efficiency 133
feed water heaters 139
relative merits of jet and surface condensers 132
theory of condenser action 123
types of 125
Corliss steam engine 37
advantages and disadvantages 39
valve mechanism 37
Crosshead and connecting rod 19
Cylinder ratios 29
Cylinders 10
D
Deep-w^ell or mine pump 69
Duplex pump 70, 71
E
Engine mechanisms, analysis of 139
crank effort 139
diagrams 140
variable thrust ^^^
INDEX
PACJE
Engine mechanisms, analysis of (continued)
fljrwheel 140
governor 146
Engine specifications 169
contract 174
drawing up si)ecifications 169
selecting an engine 169
Engine t«3ts 177
A. S. M. E. Code 177
importance of 177
method of conducting 178
F
Farm or traction engine 50
operation of plant 52
road roller tyj)e 60
semi-portable typ<i 61
Fly-ball governor 149
Flywheel 140
function 140
size of wheel 141
action of 142
Foster superh(»atcr 117
Frame 9
G
Governor 146
■ fly-ball 149
I methods of action 146
I I)endulum 147
shaft 154
i J
Jacketing 114
! jacket, function of 114
saving due to jacketing 116
L
Locomotive engines 61
boiler 61
engine charact^^ristics 64
mechanical efficiency 63
tyi>es of 65
Losses, analysis of •. 108
clearance Ill
cooling by expansion 109
exhaust waste 1 10
friction Ill
radiation 108
steam condensati(m and re-evaporation 109
INDEX
PAGE
M
Marine engines 74
auxiliary apparatus 84
condensers 86
pumps 86
reversing mechanism 84
definition of terms 74
engine details 80
bearings 82
cranks 81
crosshead guides 81
cylinder 80
marine details resemble stationary 81
management of 93
adjustments after starting 96
before starting 93
bUges 99
emergencies 102
hot bearings 97
hot rods 98
jackets 99
knocks 98
linking up 99
lubrication 97
marking off nuts 99
refitting bearings 100
starting engine 94
stopping vessel 101
methods of propulsion 75
propellers 90
screw 90
propelling action of 91
propulsion 88
economical speed 89
indicated thrust 89
resistance factors for ship in motion 88
starting 88
types of. 76
beam 75
comparison of marine with stationary types 80
cylinder 76
inclined 76
vertical 76
Mechanical and thermal efficiency 106
analysis of losses 108
losses in practical engine 107
low thermal efficiency inherent 105
Multiple expansion 112
exhaust waste utilized ^*^^
INDEX
PAQB
Multiple expansion (continued)
less condensation 112
methods of compounding 113
N
Newcomen steam engine 3
Noidberg engine 42
P
Pendulum governor 147
Piston rings 13
Pistons 13
Q
Quadruple engines 28
S
Savery steam engine 1
Separately-fired superheater 119
Shaft governor 164
Snap rings 13
Stationary engines 31
angle-compound type 39
Buckeye vertical cross-compound type 36
Corliss type 37
Nordberg engine 42
simple side-crank type 31
simple vertical type 33
advantages of vertical over horizontal type 34
disadvantages of vertical type 36
stationary types 49
Uniflow steam engine 41
Steam chest 19
Steam engines 1-192
annual operation expenses 176
compound pumping engine 7
cost of 174
development 1
early history 1
engine mechanisms, analysis of 139
engine specifications 169
erection of 158
foundations 158
installations of attachments 160
setting the engine 160
marine engine 74
mechanical and thermal efficiency 105
Newcomen 3
INDEX
PAGB
Steam engines (continued)
operation of 161
adjustment of connecting rod box 162
adjusting eccentric strap 162
care of bearing caps 161
competent engineer a requisite 161
governor 163
lining up crosshead 162
lubrication 163
starting engine 168
valve setting 163
operation economies Ill
condensers 123
jacketing 1 14
multiple expansion 112
superheating 116
parts of 7
relative cost of operation items 176
Savery 1
tests 177
types and construction * 26
Watt 6
Stuffing box and packing 14
Sub-base ^ 8
Superheaters, purposes of 120
Superheating 116
economic advantages 122
Foster superheater 117
general practice 116
separately-fired superheater 119
superheaters, purposes of 120
T
Tables
Buckeye engine, performance of 190, 191
cost of high speed, single cylinder engines 175
cost of installation and operation for one year 176
heights of governor for different speeds of engine 151
increase in efficiency by use of condenser for various engines 134
indicator diagram data for Buckeye engine test 188, 189
price of single cylinder Corliss engines, set and erected 176
Triple expansion engines 28
Types and construction of steam engines 25
classification 25
compound engines 26
farm or traction engine 50
locomotive engine 61
simple engines 26
special engines '^'^
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